This commit adds auto-configuration support for both `RestClient` and
`RestHighLevelClient` which are provided by `elasticsearch-rest-client`
and `elasticsearch-rest-high-level-client` dependencies respectively.

`RestClient` is associated with configuration properties in the
`spring.elasticsearch.rest.*` namespace, since this is the component
taking care of HTTP communication with the actual Elasticsearch node.

`RestHighLevelClient` wraps the first one and naturally inherits that
configuration.

Closes gh-12600