Closes#81652.
Convert the `repository-azure`, `repository-gcs` and `repository-s3`
plugins into modules, so that they are always included in the
Elasticsearch distribution. Also change plugin installation, removal
and syncing so that attempting to add or remove these plugins still
succeeds but is now a no-op.
Today a snapshot repository does not have a well-defined identity. It
can be reregistered with a different cluster under a different name, and
can even be registered with multiple clusters in readonly mode.
This presents problems for cases where we need to refer to a specific
snapshot in a globally-unique fashion. Today we rely on the repository
being registered under the same name on every cluster, but this is not a
safe assumption.
This commit adds a UUID that can be used to uniquely identify a
repository. The UUID is stored in the top-level index blob, represented
by `RepositoryData`, and is also usually copied into the
`RepositoryMetadata` that represents the repository in the cluster
state. The repository UUID is exposed in the get-repositories API; other
more meaningful consumers will be added in due course.
