Offline startup of the Elasticsearch backend

Currently, even when the index lifecycle strategy is set to NONE, the Elasticsearch backend will send a request to the cluster on startup in order to check the version of the cluster.
This has two purposes:

1. Check that the version of the cluster matches the version configured by the user (if any)

2. Gather more precise information about the Elasticsearch version so as to pick the appropriate protocol dialect.

In some cases, it's desirable that no request is sent to the Elasticsearch cluster on startup. We should try to get rid of this version check:

• Maybe add a configuration option to disable it explicitly? This would require that the version provided by the user is precise enough to determine the protocol dialect.

• Maybe remove the check completely when a version is specified, and is precise enough to determine the protocol dialect? That would lead to complex, potentially surprising behavior, though...

• Something else?

See https://discourse.hibernate.org/t/manual-indexing-without-listeners/3790/3