The brand guidelines for Elasticsearch use the product name as a single work. We should avoid using ElasticSearch or elasticSearch.
Fortunately, there aren't any incorrect camel-case representations in the main API, just in documentation and internal variable names. It should be a trivial fix to remove this inconsistency.
There is one test utility class https://github.com/apache/beam/blob/b23d3a60aad6280bdb2904bb295da7dcf3e708a5/sdks/java/io/elasticsearch-tests/elasticsearch-tests-common/src/test/java/org/apache/beam/sdk/io/elasticsearch/ElasticSearchIOTestUtils.java that should be renamed. A quick search doesn't reveal any use of this class outside of the Beam repository.