Allow manual respin of existing tags

[hardillb]

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)

Proposed changes

This updates the current GH Action to allow admins to re-spin an existing tagged release in order to update the underlying container layers to pick up security fixes

Discussed in https://github.com/node-red/node-red-docker/issues/367

Checklist

• [x] I have read the contribution guidelines
• [x] For non-bugfix PRs, I have discussed this change on the mailing list/slack team.
• [ ] I have run grunt to verify the unit tests pass
• [ ] I have added suitable unit tests to cover the new/changed functionality

[hardillb]

This will need porting to the dev branch ahead of 3.1 release.