make AOT hints for ELC optional

[rursprung]

spring-data-opensearch is based on spring-data-elasticsearch, however it excludes the underlying ELC dependencies since it doesn't need them.
if someone wants to use AOT (or native image) with spring-data-opensearch this automatically also enables the AOT hints coming from spring-data-elasticsearch and these then fail since the ELC dependencies are not on the classpath.

the AOT hints for ELC should be made optional, dependent on ELC being on the classpath. this has no functional impact on existing spring-data-elasticsearch consumers which already use AOT.

see opensearch-project/spring-data-opensearch#441
this is just a tracking issue for #3267
the AOT hints for spring-data-opensearch come in opensearch-project/spring-data-opensearch#638