Feat: add initial Google Drive connector support (#11147)

### What problem does this PR solve?

This feature is primarily ported from the
[Onyx](https://github.com/onyx-dot-app/onyx) project with necessary
modifications. Thanks for such a brilliant project.

Minor: consistently use `google_drive` rather than `google_driver`.

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src="https://github.com/user-attachments/assets/6f64e70e-881e-42c7-b45f-809d3e0024a4"
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src="https://github.com/user-attachments/assets/dfa7d1ef-819a-4a82-8c52-0999f48ed4a6"
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src="https://github.com/user-attachments/assets/39e792fb-9fbe-4f3d-9b3c-b2265186bc22"
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<img width="947" height="323" alt="image"
src="https://github.com/user-attachments/assets/27d70e96-d9c0-42d9-8c89-276919b6d61d"
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### Type of change

- [x] New Feature (non-breaking change which adds functionality)

common/data_source/google_util/oauth_flow.py

@@ -0,0 +1,129 @@
+import json
+import os
+import threading
+from typing import Any, Callable
+
+from common.data_source.config import DocumentSource
+from common.data_source.google_util.constant import GOOGLE_SCOPES
+
+
+def _get_requested_scopes(source: DocumentSource) -> list[str]:
+    """Return the scopes to request, honoring an optional override env var."""
+    override = os.environ.get("GOOGLE_OAUTH_SCOPE_OVERRIDE", "")
+    if override.strip():
+        scopes = [scope.strip() for scope in override.split(",") if scope.strip()]
+        if scopes:
+            return scopes
+    return GOOGLE_SCOPES[source]
+
+
+def _get_oauth_timeout_secs() -> int:
+    raw_timeout = os.environ.get("GOOGLE_OAUTH_FLOW_TIMEOUT_SECS", "300").strip()
+    try:
+        timeout = int(raw_timeout)
+    except ValueError:
+        timeout = 300
+    return timeout
+
+
+def _run_with_timeout(func: Callable[[], Any], timeout_secs: int, timeout_message: str) -> Any:
+    if timeout_secs <= 0:
+        return func()
+
+    result: dict[str, Any] = {}
+    error: dict[str, BaseException] = {}
+
+    def _target() -> None:
+        try:
+            result["value"] = func()
+        except BaseException as exc:  # pragma: no cover
+            error["error"] = exc
+
+    thread = threading.Thread(target=_target, daemon=True)
+    thread.start()
+    thread.join(timeout_secs)
+    if thread.is_alive():
+        raise TimeoutError(timeout_message)
+    if "error" in error:
+        raise error["error"]
+    return result.get("value")
+
+
+def _run_local_server_flow(client_config: dict[str, Any], source: DocumentSource) -> dict[str, Any]:
+    """Launch the standard Google OAuth local-server flow to mint user tokens."""
+    from google_auth_oauthlib.flow import InstalledAppFlow  # type: ignore
+
+    scopes = _get_requested_scopes(source)
+    flow = InstalledAppFlow.from_client_config(
+        client_config,
+        scopes=scopes,
+    )
+
+    open_browser = os.environ.get("GOOGLE_OAUTH_OPEN_BROWSER", "true").lower() != "false"
+    preferred_port = os.environ.get("GOOGLE_OAUTH_LOCAL_SERVER_PORT")
+    port = int(preferred_port) if preferred_port else 0
+    timeout_secs = _get_oauth_timeout_secs()
+    timeout_message = (
+        f"Google OAuth verification timed out after {timeout_secs} seconds. "
+        "Close any pending consent windows and rerun the connector configuration to try again."
+    )
+
+    print("Launching Google OAuth flow. A browser window should open shortly.")
+    print("If it does not, copy the URL shown in the console into your browser manually.")
+    if timeout_secs > 0:
+        print(f"You have {timeout_secs} seconds to finish granting access before the request times out.")
+
+    try:
+        creds = _run_with_timeout(
+            lambda: flow.run_local_server(port=port, open_browser=open_browser, prompt="consent"),
+            timeout_secs,
+            timeout_message,
+        )
+    except OSError as exc:
+        allow_console = os.environ.get("GOOGLE_OAUTH_ALLOW_CONSOLE_FALLBACK", "true").lower() != "false"
+        if not allow_console:
+            raise
+        print(f"Local server flow failed ({exc}). Falling back to console-based auth.")
+        creds = _run_with_timeout(flow.run_console, timeout_secs, timeout_message)
+    except Warning as warning:
+        warning_msg = str(warning)
+        if "Scope has changed" in warning_msg:
+            instructions = [
+                "Google rejected one or more of the requested OAuth scopes.",
+                "Fix options:",
+                "  1. In Google Cloud Console, open APIs & Services > OAuth consent screen and add the missing scopes "
+                "     (Drive metadata + Admin Directory read scopes), then re-run the flow.",
+                "  2. Set GOOGLE_OAUTH_SCOPE_OVERRIDE to a comma-separated list of scopes you are allowed to request.",
+                "  3. For quick local testing only, export OAUTHLIB_RELAX_TOKEN_SCOPE=1 to accept the reduced scopes "
+                "     (be aware the connector may lose functionality).",
+            ]
+            raise RuntimeError("\n".join(instructions)) from warning
+        raise
+
+    token_dict: dict[str, Any] = json.loads(creds.to_json())
+
+    print("\nGoogle OAuth flow completed successfully.")
+    print("Copy the JSON blob below into GOOGLE_DRIVE_OAUTH_CREDENTIALS_JSON_STR to reuse these tokens without re-authenticating:\n")
+    print(json.dumps(token_dict, indent=2))
+    print()
+
+    return token_dict
+
+
+def ensure_oauth_token_dict(credentials: dict[str, Any], source: DocumentSource) -> dict[str, Any]:
+    """Return a dict that contains OAuth tokens, running the flow if only a client config is provided."""
+    if "refresh_token" in credentials and "token" in credentials:
+        return credentials
+
+    client_config: dict[str, Any] | None = None
+    if "installed" in credentials:
+        client_config = {"installed": credentials["installed"]}
+    elif "web" in credentials:
+        client_config = {"web": credentials["web"]}
+
+    if client_config is None:
+        raise ValueError(
+            "Provided Google OAuth credentials are missing both tokens and a client configuration."
+        )
+
+    return _run_local_server_flow(client_config, source)