chore(MZCLD-2261): auto tag and deploy prod on merges to main

[whd]

Refractr PR Checklist

JIRA ticket: https://mozilla-hub.atlassian.net/browse/MZCLD-2261

This is the "shortest diff" approach to solving auto deploying changes on merges to main. It has potential concurrency issues that IMO are unlikely to arise in practice. I'm very open to doing this in other ways but my focus is on reducing the number of steps required of an operator to implement a redirect.

When creating a PR for Refractr, confirm you've done the following steps for a smooth CI and CD experience:

• Have you updated the relevant YAML in the PR?
• Have you checked the relevant YAML for any possible dupes regarding your domain?
• Have you checked if there are any TLS cert concerns - e.g. if the domain being redirected already exists, and it is being changed to point at refractr, is a temporary TLS 'outage' while waiting for certification via HTTP challenge okay? If not, add a note to the JIRA ticket.
• If desired, have you generated the nginx config manually to confirm updates work as expected?

After PR merge, next steps include:

• A merge to the main branch will automatically deploy refractr's stage environment -- deploying the prod environment requires a GitHub release to be created.
• Once deployed, refractr's certmap must be updated and DNS entries must be changed -- SRE can help with this. Please pull someone in on the JIRA ticket or ask for help in #sre on Slack.

[whd]

Updated to use the jbuck recommended approach: https://github.com/mozilla/global-platform-admin/pull/5551