The server-proxied upload flow (replaces presign-PUT) stores the
file-level metadata directly on the UploadSessions row at session
creation, so step 2 (PUT bytes) can build the StorageObjects row
without re-sending metadata through a separate CompleteUploadRequest.
New columns on upload_sessions:
file_name VARCHAR(255) NOT NULL DEFAULT ''
usage_type VARCHAR(32) NOT NULL DEFAULT 'working_copy'
visibility VARCHAR(16) NOT NULL DEFAULT 'private'
is_immutable TINYINT(1) NOT NULL DEFAULT 0
The SQLAlchemy model already declares these columns; this migration
applies the schema change to MySQL.
Migration: c3d4e5f6a7b8_upload_session_object_metadata.py
(chains off a2b3c4d5e6f7)
