Prior to this commit, Spring Boot would only auto-configure the
`RestHighLevelClient` and `RestClientBuilder` if the
`RestHighLevelClient` was present. This was done in 1d73d4ed.
This commit brings back the exposing of the `RestClient` bean in when
exposing the `RestHighLevelClient` or when the `RestHighLevelClient`
is not present. It allows for using the auto-configuration and its
customizers of the `RestClientBuilder` in a similar way as it is done
for the `RestTemplateBuilder` and the `WebClient.Builder`.
The presence of the `elasticsearch-rest-high-level-client` module is
now optional. This opens the door for potentially adding support for
the new Elasticsearch Java Client[1] that is based on the same
`RestClient`.
The health contributor and its configuration has also been updated to
only depend on the low-level RestClient.
See gh-28496
[1] https://github.com/elastic/elasticsearch-java
eb3bf40bdb