Enable partial updates Elasticsearch

Expose a configuration option on the ElasticsearchIO to enable partial updates rather than full document inserts.

Rationale: We have the case where different pipelines process different categories of information of the target entity (e.g. one for taxonomic processing, another for geospatial processing). A read and merge is not possible inside the batch call, meaning the only way to do it is through a join. The join approach is slow, and also stops the ability to run a single process in isolation (e.g. reprocess the geospatial component of all docs).

Use of this configuration parameter has to be used in conjunction with controlling the document ID (possible since BEAM-3201) to make sense.

The client API would include a withUseUpdate(...) such as:

source.apply(
  ElasticsearchIO.write()
    .withConnectionConfiguration(connectionConfiguration)
    .withIdFn(new ExtractValueFn("id"))
    .withUseUpdate(true)