pubsub: allow empty filter definition

[prauc]

This PR allows to define an empty filter definition, as we do for our API. The implementation is due to PR #11421, which prohibits this.

Tests added and passed.

Fixes #19269

Release Note Template for Downstream PRs (will be copied)

pubsub: fixed a validation bug that didn't allow empty filter definitions for `google_pubsub_subscription` resources

[github-actions]

Hello! I am a robot. Tests will require approval from a repository maintainer to run.

@SarahFrench, a repository maintainer, has been assigned to review your changes. If you have not received review feedback within 2 business days, please leave a comment on this PR asking them to take a look.

You can help make sure that review is quick by doing a self-review and by running impacted tests locally.

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 2 files changed, 58 insertions(+), 1 deletion(-))
google-beta provider: Diff ( 2 files changed, 58 insertions(+), 1 deletion(-))

[modular-magician]

Tests analytics

Total tests: 50
Passed tests: 48
Skipped tests: 1
Affected tests: 1

Click here to see the affected service packages

• pubsub

Action taken

Found 1 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

• TestAccPubsubSubscription_filter

Get to know how VCR tests work

[modular-magician]

$\textcolor{green}{\textsf{Tests passed during RECORDING mode:}}$
TestAccPubsubSubscription_filter[Debug log]

$\textcolor{green}{\textsf{No issues found for passed tests after REPLAYING rerun.}}$

---

$\textcolor{green}{\textsf{All tests passed!}}$

View the build log or the debug log for each test

[SarahFrench]

This looks good to me, thanks! I'm going to suggest and apply an change to remove the copyright notice before merging though

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 2 files changed, 56 insertions(+), 1 deletion(-))
google-beta provider: Diff ( 2 files changed, 56 insertions(+), 1 deletion(-))

[modular-magician]

Tests analytics

Total tests: 50
Passed tests: 49
Skipped tests: 1
Affected tests: 0

Click here to see the affected service packages

• pubsub

$\textcolor{green}{\textsf{All tests passed!}}$

View the build log