OpenAPI: Express server capabilities via /config endpoint

[nastra]

This introduces a capabilities field to the response of the /config endpoint, signaling what is being supported by the server. The current capabilities that come to mind are:

• pagination
• scan-planning
• views
• vended-credentials
• remote-signing
• oauth2
• sigv4

Capabilities like scan-planning / views / remote-signing / oauth2 would indicate that certain endpoints are implemented by the server and can be safely called by clients. Other capabilities would reflect using a certain query param or sending a particular header by a client to the server.

Using tags allows to group endpoints in the Swagger UI:

For scan-planning it's not clear yet whether whether we'd like to only have scan-planning or whether there should also be scan-pre-planning, so it's best to introduce this capability as part of https://github.com/apache/iceberg/pull/9695 (cc @rahil-c)