Add GCE Zonal Reservation resource

[rileykarson]

Fixes hashicorp/terraform-provider-google#4254

The test fails right now due to a canonicalisation issue with min_cpu_platform. Holding until that's fixed, but pushing so I don't forget about the branch.

Release Note for Downstream PRs (will be copied)

`google_compute_reservation` allows you to reserve instance capacity in GCE.

[modular-magician]

Hi! I'm the modular magician, I work on Magic Modules.
This PR seems not to have generated downstream PRs before, as of 4736a3bcaff4f570d6cf2c732aee8e5370a087f9.

Pull request statuses

No diff detected in Ansible.
No diff detected in Inspec.

New Pull Requests

I built this PR into one or more new PRs on other repositories, and when those are closed, this PR will also be merged and closed.
depends: hashicorp/terraform-provider-google-beta#1086
depends: GoogleCloudPlatform/terraform-google-conversion#178
depends: hashicorp/terraform-provider-google#4332

[modular-magician]

Hi! I'm the modular magician, I work on Magic Modules.
I see that this PR has already had some downstream PRs generated. Any open downstreams are already updated to your most recent commit, 9d40ec9.

Pull request statuses

terraform-provider-google-beta already has an open PR.
terraform-google-conversion already has an open PR.
terraform-provider-google already has an open PR.
No diff detected in Ansible.
No diff detected in Inspec.

New Pull Requests

I didn't open any new pull requests because of this PR.

[modular-magician]

Hi! I'm the modular magician, I work on Magic Modules.
I see that this PR has already had some downstream PRs generated. Any open downstreams are already updated to your most recent commit, f41316d.

Pull request statuses

terraform-provider-google-beta already has an open PR.
terraform-google-conversion already has an open PR.
terraform-provider-google already has an open PR.
No diff detected in Ansible.
No diff detected in Inspec.

New Pull Requests

I didn't open any new pull requests because of this PR.