Add support for source fetching + building

[chancila]

Right now bazelisk fetches binary distributions via github releases, I'm curious if adding support for source based fetching + building is something being considered or would be okay to contribute?

Perhaps some extra syntax in .bazelversion that instructs bazelisk to fetch a zip of some given sha/tag and build a release of bazel locally, and use that as the underlying bazel binary.

[philwo]

This is a nice idea. I won't have time to work on it in the next weeks, but I generally think it would be cool to have. :)

[chancila]

great, was just checking if the project is receptive to it, I can work on a PR for this