Remove set-automatic-deploys GitHub action

Description:

- At current the `set-automatic-deploys-enabled` is broken as there is no corresponding event binding so when a POST request is made from the `set-automatic-deploy` GitHub action` nothing happens
- Discussed with @theseanything that maintaining this workflow is too cumbersome since we infrequently disable automatic deploys. So a decision has been made to remove the workflow and instead ask developers to update `govuk-helm-charts/image-tags` manually