Deprecate elasticsearch connection

[tobio]

Configuring provider connection configuration on a per-resource basis isn't supported during import operations, and duplicates the core Terraform aliases provider functionality.

Marking these attributes as deprecated as the first step to removing them in a future version of the provider.

Related to #203

[webfella]

🎉

Big 👍👍 for adding the guide for multiple deployments too mate!

[orlandothoeny]

This change makes it impossible to create a new ec_deployment instance + resources like an Elasticsearch User inside a single module without ugly workarounds

[orlandothoeny]

Got it to work using

provider "elasticstack" {
  elasticsearch {
    endpoints = [ec_deployment.deployment.elasticsearch.https_endpoint]
    username  = google_secret_manager_secret_version.root_user.secret_data
    password  = google_secret_manager_secret_version.root_password.secret_data
  }
}

However, had to manually remove the existing user resource from the state, always got an authentication error before.

[mveroone]

Got it to work using

provider "elasticstack" {
  elasticsearch {
    endpoints = [ec_deployment.deployment.elasticsearch.https_endpoint]
    username  = google_secret_manager_secret_version.root_user.secret_data
    password  = google_secret_manager_secret_version.root_password.secret_data
  }
}

However, had to manually remove the existing user resource from the state, always got an authentication error before.

That won't work if you're creating an undetermined number of deployments in the code and create elasticstack resources over all of them, while elasticsearch_connection does.

I disagree on the initial premise of this PR that the behavior "Duplicates core terraform provider alias feature". It allows for more. Platform-engineering using both providers will be a nightmare without that per-resource block.