build: convenience script for analyzing an Envoy commit range

Many organizations regularly pull in Envoy changes and run them. The project has grown quite a bit however, and a weeks worth of changes can easily be 100+ commits. Many of these commits don't actually matter to the organization that pulls them in. I think we can create a script using a combination of Python/Bazel that would do something like the following:

• Take a commit range as an argument
• Take a set of extensions that the user cares about
• Filter all commits down to the set of commits that a) touch core code and b) touch extensions that the user cares about.

The output can then be a list of commits, optimally in summary form with links to click on for more info (perhaps output as an HTML page).

This would allow organizations to better analyze the commits they are bringing in and understand the risk of those commits to their deployment.