Automate the release process

[NimJay]

Background

• Last year (2022), we made 9 Online Boutique releases.
• Ideally, we would release more often (for instance, 1 release per month).
• Currently, the release process is documented at /hack/.
• Creating a new release takes more than 1 hour (waiting for images to build, composing release notes, sending Google-internal release email, dealing with any bugs such as this, updating onlineboutique.dev etc.).

Feature Request

• We should automate the release process.
• This will:
  • Speed up the release process and enable us create more frequent releases.
  • Make it possible for non-TLs to create a new release.

Additional Info

• The new automation should use Google Cloud Build — not GitHub Actions — since migrating to Google Cloud Build is an Online Boutique goal.

[NimJay]

Update to cool down out-of-SLO list: no work has been started.