Feat: add IMAP data source integration with configuration and sync capabilities (#12316)

### What problem does this PR solve?
issue:
#12217 [#12313](https://github.com/infiniflow/ragflow/issues/12313)
change:
add IMAP data source integration with configuration and sync
capabilities

### Type of change

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

common/data_source/__init__.py

@@ -38,6 +38,7 @@ from .webdav_connector import WebDAVConnector
 from .moodle_connector import MoodleConnector
 from .airtable_connector import AirtableConnector
 from .asana_connector import AsanaConnector
+from .imap_connector import ImapConnector
 from .config import BlobType, DocumentSource
 from .models import Document, TextSection, ImageSection, BasicExpertInfo
 from .exceptions import (
@@ -75,4 +76,5 @@ __all__ = [
     "UnexpectedValidationError",
     "AirtableConnector",
     "AsanaConnector",
+    "ImapConnector"
 ]