Migrate off probot-CLA to new GitHub Action

[cursedcoder]

Hello 👋

We are deprecating probot usage, so all Shopify repos should be migrated to use new GitHub CLA Action.

You can see how this works in vscode-shopify-ruby repo.

If you have any questions, please reach us on Slack.

After you merge this PR, make sure to update branch protection settings (if you have any):

1. Go to Settings > Branches > Edit main (or any default) branch
2. Remove the CLA check from probot (click x):
3. Add CLA check from GitHub action:

[alinebee]

After you merge this PR, make sure to update branch protection settings (if you have any)

I'm not on a team that owns this repo (I've only contributed a PR or two) and don't have access to the settings for this repo.

I'm not actually sure which team does own this, which may mean it's unowned. Are you able to access the settings screen yourself @cursedcoder?

[cursedcoder]

@alunbestor there are no branch protection rules on this repo, so it's not needed