Write a script to simplify deployments and rollbacks

Our deploy process is longer than it should be, because it involves going through a sequence of actions on Github Web UI.

Instead we can leverage the command line using git, github cli, and/or directly calling the github API, to make it easier.

Some tips:

* generate a changelog (assumes `moz` is the upstream remote -- can we infer that?)

```
git fetch moz
git log --oneline --first-parent moz/production..moz/main | awk '{ $1 = "*"; print }'
```

* checks that production doesn't have any unwanted commit

```
git fetch moz
git log --oneline moz/main..moz/production --no-merges
```

* create a production deployment PR with the github cli

```
gh pr create --base production --head main -t "Deploy XXX" -b "body"
```

(would be good to put the result of "changelog" in the body)

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-318)