Required for HSEARCH-3523.
Part of the metadata building in the Elasticsearch backend depends on the dialect, which depends on the version of Elasticsearch running on the cluster. That's why we currently make an API call to the cluster to determine the version, and then the dialect.
But with we will need to postpone any kind of communication with the Elasticsearch cluster to the second phase of the build, while we will need to build metadata during the first phase of the build.
There's a chicken-and-egg problem here, which we have to solve by asking the user to specify the Elasticsearch dialect to use explicitly, before the first phase of the boot. That way, we don't need to make an API call to the ES cluster to determine the version.