Allow Bazelisk to be more general

Was hoping to allow bazelisk to install a bazel binary from a repo that is not a fork of bazel but a different repo and doesn't have the same name (bazel).

This issue is just asking if you would be open to prs with this goal.
The defaults would stay the same and there would be no changes for other users who did not want these features.

Thank you for considering :)

The issue names no files, tests, or entry points. First clarify the configuration and repository behavior needed for installing a Bazel binary from a differently named, non-fork repository; done means the new option works while existing defaults and users remain unchanged.

Written by the indexing model from the issue text.