Expand configuration for Elastic to support serverless

Is your feature request related to a problem? Please describe.

We were looking to use Elastic's serverless option for our visibility store, but to connect we would need to set an Authorization header, which currently doesn't appear to be supported by the config for the ES client: https://github.com/temporalio/temporal/blob/66ab754e7e8d60421678457df1914fa7ddae9dc3/common/persistence/visibility/store/elasticsearch/client/config.go#L45-L60

Describe the solution you'd like

I'd like to be able to add a configuration like the following:

elasticsearch:
  # ...
  headers:
    Authorization: "ApiKey {{ .Env.TEMPORAL_ES_VISIBIILITY_STORE_PASSWORD }}"

Describe alternatives you've considered

Another option would be to have this kind of a format:

elasticsearch:
  # ...

  auth:
    basic:
      username: "..."
      password: "..."
    # or
    elastic:
      apiKey: "..."

But it feels far less flexible and a bit more complicated to implement.

Other than that, I can't really think of any alternative, besides having to set up a proxy that adds the header. Ideally, we avoid the operational overhead of another proxy and just do it straight on the client.

Start with common/persistence/visibility/store/elasticsearch/client/config.go at the configuration section linked in the issue, then trace how those settings reach the Elasticsearch client. Add support for configuring request headers and verify that the Authorization header is accepted and used when connecting to the visibility store.