Automate setting 'Synapse-Indexed' for new indexed externally-hosted datasets

[aclayton555]

Emerges from: https://sagebionetworks.slack.com/archives/C02LPNCD1LL/p1780972873321129

Per Aditya: At this point we still have to manually set the GEO datasets indexed on Synapse to Synapse Indexed

Can we explore ways to automate this as we scale generating Synapse-indexed, Geo hosted datasets (via #228 )