Add resource to get User ID of currently used user

[thevops]

Feature Description

When I want to create a new API Key for my own user (key type: USER), I have to give user_id, but it's not possible to get it while having Full platform user. Only Admin can do this (I tried this https://docs.newrelic.com/docs/apis/rest-api-v2/account-examples-v2/listing-users-your-account/).

Of course, I can find my user_id by data source, but it requires authentication_domain_id which is also not available for me as Full platform user.

Please, create another resource (e.g. newrelic_user_current) which returns the user object for the credentials that are currently used by Terraform.

Describe Alternatives

It's probably a bug, because I can find my user ID by:

1. Manually create API key (type: USER) in New Relic UI.
2. Write code for the above resource (resource "newrelic_api_access_key" "...."), but don't use user_id argument.
3. Import the above resource to the Terraform state.
4. Read the user_id from the state (e.g. as JSON).

Now, you can use user_id in the other newrelic_api_access_key resources.

Using the above way, you can get a User ID of any other user. The only need is to be able to see API Keys in New Relic UI.