Fix blob sync: skip unsupported files before download (#14357)

### What problem does this PR solve?

Blob storage sync was downloading unsupported files first and rejecting
them later, which wasted bandwidth and made sync slower. This PR skips
unsupported extensions before download and applies `allow_images` in
blob sync. fixes #14338

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

common/data_source/blob_connector.py

@@ -10,6 +10,7 @@ from common.data_source.utils import (
     download_object,
     extract_size_bytes,
     get_file_ext,
+    is_accepted_file_ext,
 )
 from common.data_source.config import BlobType, DocumentSource, BLOB_STORAGE_SIZE_THRESHOLD, INDEX_BATCH_SIZE
 from common.data_source.exceptions import (
@@ -18,7 +19,7 @@ from common.data_source.exceptions import (
     CredentialExpiredError,
     InsufficientPermissionsError
 )
-from common.data_source.interfaces import LoadConnector, PollConnector
+from common.data_source.interfaces import LoadConnector, OnyxExtensionType, PollConnector
 from common.data_source.models import Document, SecondsSinceUnixEpoch, GenerateDocumentsOutput
 
 
@@ -130,15 +131,23 @@ class BlobStorageConnector(LoadConnector, PollConnector):
 
         # Collect all objects first to count filename occurrences
         all_objects = []
+        extension_type = OnyxExtensionType.Plain | OnyxExtensionType.Document
+        if bool(self._allow_images):
+            extension_type |= OnyxExtensionType.Multimedia
         for page in pages:
             if "Contents" not in page:
                 continue
             for obj in page["Contents"]:
-                if obj["Key"].endswith("/"):
+                key = obj["Key"]
+                if key.endswith("/"):
                     continue
                 last_modified = obj["LastModified"].replace(tzinfo=timezone.utc)
-                if start < last_modified <= end:
-                    all_objects.append(obj)
+                if not (start < last_modified <= end):
+                    continue
+                file_name = os.path.basename(key)
+                if not is_accepted_file_ext(get_file_ext(file_name), extension_type):
+                    continue
+                all_objects.append(obj)
         
         # Count filename occurrences to determine which need full paths
         filename_counts: dict[str, int] = {}