Add TeamCity testing project for ephemeral resources feature branch, clean up imports

[modular-magician]

Adding projects in our TeamCity environment for testing ephemeral resources

This project will:

• Use a more recent Terraform binary version that contains the ephemeral feature
  • See EphemeralResourcesTfCoreVersion
• Have builds only for services were we're adding ephemeral resources
• Have builds that allow using the hashicorp and modular-magician owned repos (can test PRs pre-merge)
• CRON triggers to schedule builds (that use the hashicorp repo) every night

Preview of the changes

Here is a test project where this PR's config is deployed: https://hashicorp.teamcity.com/project/TerraformProviders_TerraformProviderGoogleSarahCheckingEphemeralTesting?mode=builds

This is what the new addition to TeamCity will look like - we only need to test the resourcemanager package as all ephemeral resources we want to add are in that package:

Here's a look at the trigger set on the builds using the HashiCorp-owned repos:

Release Note Template for Downstream PRs (will be copied)

Derived from GoogleCloudPlatform/magic-modules#11847