refactor: Update GitHub connector to use gitingest CLI

- Refactored GitHubConnector to utilize gitingest CLI via subprocess, improving performance and avoiding async issues with Celery.
- Updated ingestion method to handle repository digests more efficiently, including error handling for subprocess execution.
- Adjusted GitHub indexer to call the new synchronous ingestion method.
- Clarified documentation regarding the optional nature of the Personal Access Token for public repositories.

surfsense_backend/app/utils/validators.py

@@ -530,7 +530,10 @@ def validate_connector_config(
         #     "validators": {},
         # },
         "GITHUB_CONNECTOR": {
-            "required": ["GITHUB_PAT", "repo_full_names"],
+            # GITHUB_PAT is optional - only required for private repositories
+            # Public repositories can be indexed without authentication
+            "required": ["repo_full_names"],
+            "optional": ["GITHUB_PAT"],  # Optional - only needed for private repos
             "validators": {
                 "repo_full_names": lambda: validate_list_field(
                     "repo_full_names", "repo_full_names"