[tda] code to get latest mobile release from monorepo

[realkosty]

Background

We want this so that we are able to move mobile repos into empower.
As you can tell by reading the code this is a bit hacky since GitHub doesn't seem to order release versions/tags very well when using <platform>-1.2.3 format. It has been useful to have release history for debugging purposes and release notes. but not sure if it's worth making it work properly or whether we should just have 1 latest release version at a time for each platform.
If there is a release version format that GitHub understands and sorts correctly (alphanumeric) - this would be easier, but I spent a good 20 minutes researching and wasn't able to find such format

Testing

1. Change code:

GITHUB_REPOS = {
    ...
    'ios': 'empower'
}

2. Create some test releases in empower
3. Run

python3 ./latest_github_release.py ios
ios-0.0.23

[asottile-sentry]