Rate limit github clone calls

[cbrand]

Description

Fixes #139.

Add rate limiting to github clone calls, avoiding issues with github "permission denied" and EOF errors when cloning too many repositories in parallel.

TODOs

Read the Gruntwork contribution guidelines.

• [x] Update the docs.
• [x] Run the relevant tests successfully, including pre-commit checks.
• [x] Ensure any 3rd party code adheres with our license policy or delete this line if its not applicable.
• [x] Include release notes. If this PR is backward incompatible, include a migration guide.

Release Notes

Added

• Rate limiting Github Clone calls to 4 per default, allows being parametrized by the --max-concurrent-clones flag

Migration Guide

None needed