Load blob commit message asyncronously

Problem to solve

For large repositories with thousands of files, find the most recent commit message is expensive. If the file was changed recently, it is a relatively cheap operation, but if it was 4 years ago it could take multiple seconds. We should avoid blocking the page with this information.

The content of the file should always be pretty fast to retrieve, so don't block on that.

Further details

Example blob link: https://gitlab.com/gitlab-org/gitlab/-/blob/master/.foreman

Proposal

Load commit messages async. Don't block the page.