feat: Add Google Access Token support for GCP actions

[tfhartmann]

Introduce a Google Access Token field extension for GCP authentication and enable the usage of user OAuth tokens in GCP actions. This enhances flexibility in authentication methods for GCP services.

Please do give this a through review, as I leaned pretty heavy on AI to write this.

[tdabasinskas]

Nice work on this overall — the feature's useful. The main thing I'd want sorted before merge is how the access token is handled. There are a couple of spots where it can end up persisted, and one option that doesn't actually work.

First, the field extension calls both setSecrets and onChange(token). setSecrets is the right one — scaffolder secrets stay in memory and aren't persisted. But onChange(token) writes the token into the form value (parameters.googleToken), and parameters do get saved to the scaffolder database. The hidden widget and review.show: false only hide it in the UI, not in storage. Can we drop the onChange call and rely just on setSecrets?

Same thing with the explicit token action input — action inputs are part of the saved task spec, and the README example feeds it from ${{ parameters.googleToken }}, which is persisted. I'd lean toward dropping the token input entirely and just reading ctx.secrets.googleAccessToken. It keeps one safe path and removes the footgun.

Last one: the secretKey option doesn't work end to end. The field lets you rename the key via ui:options.secretKey, but auth.ts hardcodes secrets.googleAccessToken. So if anyone sets a custom key, the action never finds the token and silently falls back to ADC — no error, just the wrong identity. Simplest fix is probably to drop the option and always use googleAccessToken.

I also regenerated yarn.lock and downgraded backend-plugin-api, as CI was failing.

[tfhartmann]

Awesome I'll work on these updates and push em to the branch!

[tfhartmann]

@tdabasinskas take a look at this and let me know what you think. I was able to test in my sandbox and was able to create all 3 resources! 🎆

[tdabasinskas]

Thanks! Appreciate the contribution!