Conventional commit aid

**Is your feature request related to a problem? Please describe.**
I would like to easily perform conventional commits (ideally with gitmojis) using GitUI.

**Describe the solution you'd like**
I would like an option to enable something like the [VSCode Conventional Commits](https://marketplace.visualstudio.com/items?itemName=vivaxy.vscode-conventional-commits) plugin, that prompts the user for the scope, etc. and builds the commit message from that.

Some [custom command](https://gist.github.com/timhagel/28ae03354a85ce3e5237b308912b9b52) support could also be implemented but I understand that would be a lot harder and maybe even out of scope for the project.

**Describe alternatives you've considered**
I could type them by hand, but I'd probably mess up (and wouldn't remember all the gitmojis). I could also try to find a CLI tool to do it and commit outside of GitUI, but it would mess up the workflow. Maybe gitmoji support would be sufficient.