Move 'get_project_base_directory' to common directory (#10940)

### What problem does this PR solve?

As title

### Type of change

- [x] Refactoring

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

common/file_utils.py

@@ -0,0 +1,33 @@
+#
+#  Copyright 2025 The InfiniFlow Authors. All Rights Reserved.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+
+import os
+
+PROJECT_BASE = os.getenv("RAG_PROJECT_BASE") or os.getenv("RAG_DEPLOY_BASE")
+
+def get_project_base_directory(*args):
+    global PROJECT_BASE
+    if PROJECT_BASE is None:
+        PROJECT_BASE = os.path.abspath(
+            os.path.join(
+                os.path.dirname(os.path.realpath(__file__)),
+                os.pardir,
+            )
+        )
+
+    if args:
+        return os.path.join(PROJECT_BASE, *args)
+    return PROJECT_BASE