Terraform: Pubsub Topic labels update

[drebes]

Fixes hashicorp/terraform-provider-google#3210

It's not documented that Pubsub Topics support PATCH/update, but they do.

$ make testacc TEST=./google TESTARGS='-run=TestAccPubsubTopic_update'
==> Checking source code against gofmt...
==> Checking that code complies with gofmt requirements...
TF_ACC=1 TF_SCHEMA_PANIC_ON_ERROR=1 go test ./google -v -run=TestAccPubsubTopic_update -timeout 240m -ldflags="-X=github.com/terraform-providers/terraform-provider-google/version.ProviderVersion=acc"
=== RUN   TestAccPubsubTopic_update
=== PAUSE TestAccPubsubTopic_update
=== CONT  TestAccPubsubTopic_update
--- PASS: TestAccPubsubTopic_update (15.73s)
PASS
ok  	github.com/terraform-providers/terraform-provider-google/google	15.776s

[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 fd9f9f66a15e003f704e7b826dafcc2b6b4c9118.

Pull request statuses

No diff detected in terraform-google-conversion.
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#832
depends: hashicorp/terraform-provider-google#3828
depends: modular-magician/ansible#274

[chrisst]

Given the custom update encoder I'm not sure if this will work right away with Ansible so adding @rambleraptor to the review as well.
It looks like the whole object is wrapped inside topic for the update to work.

[chrisst]

Terraform code looks good tho!

[chrisst]

@drebes can you deal with the merge conflicts and I'll merge this

[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, fc0b5f5.

Pull request statuses

terraform-provider-google-beta already has an open PR.
terraform-provider-google already has an open PR.
Ansible already has an open PR.
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: GoogleCloudPlatform/terraform-google-conversion#109

[drebes]

Done, good to merge.