Add OpenAPI annotations to miscellaneous v2 coll/core APIs

SOLR-16346 introduced a build integration to produce an OpenAPI spec, but it did little to decorate individual APIs with metadata and documentation that would be picked up by that approach. Individual APIs themselves still need annotated. (See SOLR-16380 for a discussion of the benefits of doing this.)

This ticket targets any Solr APIs not targeted explicitly by other SOLR-16380 subtasks. This includes but isn't limited to:

• /replication
• task-list and task-deletion APIs
• core/collection healthcheck and ping APIs