process refinement: auto deploy from a different branch than "main"

To facilitate review by @mr-c and others, we should stop auto deploying from the `main` branch and create a single `release` branch (or other similar name) that deployments to https://www.commonwl.org/user_guide happen from.

This would enable me and others to batch up reviews for weekly or twice-monthly review + deployment cycles.

Especially for Outreachy, this will enable @swzCuroverse and @tetron to process contributions without needing to wait for me.

This is also an opportunity to be thoughtful about the releases; for example confirming that existing links aren't broken.

Once this is setup , I will adjust merge permissions and I'll probably unsubscribe from most notifications so that @tetron and @swzCuroverse can focus on Outreachy.

- [x] create `release` branch
- [x] update deployment script to use `release` instead of `main`
- [x] Upgrade @tetron's permissions
- [ ] Document release process