Jupyter Controller edge exposed gateway-metadata endpoint that bundle builder can not fulfill

Currently investigating which charm is supposed to fulfill that endpoint, till then

https://test-observer.canonical.com/#/charms/406300?testExecutionId=473506&testResultId=10532168

Start by reviewing the linked Test Observer execution and result for charm 406300, then trace how the Jupyter Controller edge exposes the gateway-metadata endpoint and how the bundle builder fulfills it. Done means identifying which charm should provide the endpoint and resolving or documenting the fulfillment gap.

Written by the indexing model from the issue text.