enable custom commit message

- `all-contributors-cli` version: latest
- `node` version: latest
- `npm` (or `yarn`) version: latest

Relevant code or config

```json
// .all-contributorsrc
...
"commit": true,
...
```

What you did: add or update a contributor

What happened: commintlint report an error 'cause the commit message not match some rules.

Reproduction repository: -

Problem description: there's no config to replace the default commit message.

Suggested solution: add a new config let's say `commitMessage` to replace default commit message.