ci: add release action and scripts

[devisscher]

This PR adds a GH action which watches merges to the main branch. It creates a new version when changesets are detected and bumps the version accordingly.

Typical flow:

Feature work

1. Changes are made in a working branch and it is deemed that a version (patch/minor/major) bump is needed.
2. On the working branch run yarn changeset and completes the prompts.
3. Then push the generated changesets to your working branch.
4. Merge working branch as you would normally, after getting reviews and CI passes.

New version and releasing

1. When feature work is merged into main there is a release GitHub action which will run.
2. It runs yarn version and incorporates the changesets into the changelog.
3. It bumps the version accordingly. If changesets contain minor changes then the minor version is bumped.
4. The release action runs yarn release, which runs the tag command because we are using a different tool (Shipit), to publish our package. It creates a vX.X.X tag, which can then be picked up by Shipit.

The tag command creates git tags for the current version of all packages. The tags created are equivalent to those created by changeset publish, but the tag command does not publish anything to npm.

This is helpful in situations where a different tool, such as pnpm publish -r, is used to publish packages instead of changeset. For situations where changeset publish is executed, running changeset tag is not needed.

The git tags in monorepos are created in the format pkg-name@version-number and are based on the current version number of the package.json for each package. Note that in single-package repositories, the git tag will include v before the version number, for example, v1.0.0. It is expected that changeset version is run before changeset tag, so the package.json versions are updated before the git tags are created.

Safety check: when running without any version bumps:

[carrotderek]

👍🏼

[devisscher]

https://github.com/Shopify/core-issues/issues/40727