Jetpack changelog script - commit new changelog right away

### Impacted plugin

None / Other

### What

Commit new changelog entry created with `jetpack changelog` right away

### How

Let's assume folks are in the right branch, ready to continue by committing the changelog they just created.

Now we commit changelogs manually:
```sh
$ jetpack changelog add
...
Command 'add' for plugins/jetpack completed succesfully!

$ git add .
$ git commit -m "Changelog"
```

I'd expect the script to do it for me to save few commands:
```sh
$ jetpack changelog add
...
Changelog for plugins/jetpack added, and commited to the current branch.
```

If you need an escape hatch, just:

```sh
jetpack changelog add --no-commit
```

Start at the `jetpack changelog add` command entry point and trace how the changelog is created and how the current branch is committed. Compare the requested default commit behavior with `--no-commit`; done means the command commits the new changelog by default while preserving the opt-out.】【。} bereiken񟟂

Written by the indexing model from the issue text.