Migrate Autopublishing to GCB

[sealesj]

Initial testing configuration for autopublishing to use Google Cloud Build.

This change requires the pub.dev publishing to migrate into a Google Cloud Build configuration file which is triggered by a flutter GCP trigger. The tagging in the release.yml will continue to execute, and the tagging push will trigger the GCB yaml.

In this state, the current autopublishing flow would still be enabled, but we could move forward with providing access to the flutter-infra GCP project to impersonate a service account for releasing

Addresses: https://github.com/flutter/flutter/issues/126827

If you had to change anything in the flutter/tests repo, include a link to the migration guide as per the breaking change policy.

Pre-launch Checklist

• [x] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [x] I read the Tree Hygiene wiki page, which explains my responsibilities.
• [x] I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• [x] I signed the CLA.
• [x] The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• [x] I listed at least one issue that this PR fixes in the description above.
• [x] I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• [x] I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• [x] I updated/added relevant documentation (doc comments with ///).
• [x] I added new tests to check the change I am making, or this PR is test-exempt.
• [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[flutter-dashboard[bot]]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie or stuartmorgan on the #hackers channel in Chat (don't just cc them here, they won't see it! Use Discord!).

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[sealesj]

@godofredoc would flutter-infra be an appropriate project to re-use for configuring a service account to use this yaml?

[godofredoc]

@godofredoc would flutter-infra be an appropriate project to re-use for configuring a service account to use this yaml?

No, we need to create a new project for this.

[sealesj]

No, we need to create a new project for this.

Ok, the changes should be pretty straightforward on the project, ~~but I don't have the necessary permissions to make a new GCP project in the flutter parent organization~~

I'll make a new GCP project and see how far I can get with configuring the service account on that

[stuartmorgan-g]

Update from triage: this is blocked on repo tooling work. I hope to spend some time on that this month.

[stuartmorgan-g]

@sealesj What's the next step here now that the tool support has landed?

[sealesj]

@stuartmorgan Thank you for following up. I've added this to my to-do list and will be working on it soon as a P2 task

[stuartmorgan-g]

From triage: Is this still in development, or was it impacted by team changes?

[christopherfujino]

From triage: Is this still in development, or was it impacted by team changes?

TIL about this. Gonna close this as I don't plan to implement it. Feel free to re-open if you think there's value and something we should work on this year.