DXCDT-246: Add new resource to manage enabled clients on a connection

[sergiught]

🔧 Changes

It has been requested through #281 to have an easier way to manage enabled_clients on a auth0_connection resource so this PR introduces a brand new resource auth0_connection_client that does exact and only that.

To note however that using both the enabled_clients on the auth0_connection and this new auth0_connection_client resource will result in unpredictable behavior and it is discouraged. To not introduce breaking changes we'll allowing for both ways of setting enabled clients to coexist. If problematic however, the enabled_clients property on the connection might be changed to read only in the future.

The new resource has no optional fields and if either the client_id or connection_id is changed, this will force the destruction of the old resource and create a new one. On the connection level, this means that the old client_id will get removed from the enabled_clients and the new one added.

📚 References

• Redesign connection-client association to be controlled via its own resource (instead of only by the connection) #281
• Generated Docs -> https://github.com/auth0/terraform-provider-auth0/blob/61b405fe8a783e25b903a410eeb6d93700d1615e/docs/resources/connection_client.md

🔬 Testing

Other than the automated tests that were added, this can also be tested through running make install VERSION=XX.XX.XX and then using that in your terraform config as follows:

terraform {
  required_providers {
    auth0 = {
      source  = "auth0/auth0"
      version = "XX.XX.XX"
    }
  }
}

provider "auth0" {
  debug = "true"
}

resource "auth0_connection" "my_conn" {
  name     = "My-Auth0-Connection"
  strategy = "auth0"
  # Avoid using the enabled_clients = [...],
  # if using the auth0_connection_client resource.
}

resource "auth0_client" "my_client" {
  name = "My-Auth0-Client"
}

resource "auth0_connection_client" "my_conn_client_assoc" {
  connection_id = auth0_connection.my_conn.id
  client_id     = auth0_client.my_client.id
}

📝 Checklist

• All new/changed/fixed functionality is covered by tests (or N/A)
• I have added documentation for all new/changed functionality (or N/A)

[drhagen]

I don't know any Go, so I'll have to trust your implementation, but the design looks appropriate for our needs. Thanks for implementing this!

[willvedd]

@sergiught and I reviewed together 👍