GitHub Action to update manifests

[ssoriche]

When a pull request changes, or merges, checkout the metacpan-k8s repository and set the image tag used for the deployment of the web app.

Manifests updates during pull request creation or changes ensures that the process continues to work. When the change lands on the trunk branch of the repository is the update sent to the metacpan-k8s repository.

The GitHub Application for metacpan is able to bypass the pull request and commit to main, in the metacpan-k8s repository setting.