[supply] return android rollout percentages

[brainbicycle]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I see several green ci/circleci builds in the "All checks have passed" section of my PR (connect CircleCI to GitHub if not)
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.
• I've added or updated relevant unit tests.

Motivation and Context

Resolves this discussion: #19432

Android rollouts can be updated via the supply command but as far as I can tell there is no way to retrieve current rollout information for a given track or release. This makes it difficult to automate a rollout strategy, for example we would like to have a release initially rollout to 10% of users the next day 20% the next day 50% and finally 100%. Since app reviews are unpredictable it is difficult or impossible to do this on a set timeline unless we can fetch the current rollout percentage.

If I missed a way to retrieve this information already please let me know!

Description

Adds a new command google_play_track_rollout_percentages(track: 'production') that returns a list of rollout percentages for the given track. Heavily inspired / copied from existing commands google_play_track_version_codes and google_play_track_release_names

Testing Steps

I tested this locally:

1. Installed my updated fastlane as a gem in our repo
2. Created a build in a test track in google play initiallly rolled out to 10% of users
3. Created a lane that called the new command and updated this track based on roll out strategy: https://github.com/artsy/eigen/pull/10244/files