GitHub Actions workflow for a weekly scheduled update of available templates and actions

[linear]

• Actions API calls: remove authentication
• Templates API call: add authentication using a specialized app.openops.com user account
• Create a repo secret with user credentials
• Templates API call: get credentials locally or from the repo secret
• Create one GitHub Actions workflow that runs weekly or on demand; only creates a PR to the base branch if there are Git changes after running the two scripts; otherwise completes successfully with an informative message

[linear]

DOC-146