[DPE-1577] Supporting storage locations and migration OOP models

[BryanFauble]

Problem:

Storage locations and migration functions were not ported over into the OOP models — users had to use the legacy synapseclient and synapseutils threading-based API to configure storage locations or migrate files between them.

Solution:

1. Added StorageLocation model with store_async / get_async support, covering all location types: Synapse S3, External S3, GCS, SFTP, HTTPS, External Object Store, and Proxy servers
2. Added StorageLocationConfigurableMixin on Project and Folder so storage locations can be set directly from those entities
3. Added async migration.py service with SQLite-backed indexing and multipart_copy_async for migrating files between storage locations, replacing the threading-based synapseutils.migrate_functions
4. Fixed StorageLocationType disambiguation: SFTP and HTTPS share the same concreteType, now resolved via (concreteType, uploadType) tuple lookup

Testing:

1. Unit tests added for StorageLocation, migration, migration_types, and storage_location_services
2. Integration tests added covering SYNAPSE_S3, External S3 (requires AWS credentials), GCS (requires google-cloud-storage), and project/folder storage location assignment