WebIDE: Make Ctrl+Enter automatically commit when commit textarea is focused

What does this MR do?

This MR makes typing Ctrl+Enter while the commit message textarea is selected in WebIDE automatically submit the commit message. It's a small shortcut that can help

What are the relevant issue numbers?

#46544 (closed)

Does this MR meet the acceptance criteria?

I prefer not to check anything here, feel free to check what I should have checked !

• Changelog entry added, if necessary
• Documentation updated
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides

This is my first contribution, I hope I'm doing things correctly. If not, let me know!

cc: https://gitlab.com/gitlab-com/marketing/community-relations/contributor-program/gitlab-hackathon/q4-2018-hackathon/issues/1