[Feature] Kibana connection configuration in elasticstack provider block should also support "bearer_token" for JWT auth.

[santhoshza]

Is your feature request related to a problem? Please describe.
We are trying to create fleet resources through IaaC and will only need kibana connection block. We are using JWT token to authenticate with the cluster. Since the kibana connection doesn't support bearer_token, we are forced to use elasticsearch configuration block as well and grant additional cluster level privileges to JWT token so that it can successfully authenticate.

Describe the resource you would like to have implemented.
Kibana connection configuration block should also support "bearer_token" authentication. At the moment it only supports api_key & username auth.

Describe the solution you'd like
bearer_token auth support for jwt authentication.

Describe alternatives you've considered
We have granted additional privileges to JWT token and used elasticsearch connection block to authenticate.

Additional context
Add any other context or screenshots about the feature request here.