Make `git-risk` mark tickets automatically that are at risk using the github API

We should utilize ticketing system APIs to automatically mark tickets in a consistent manner that could be "at risk" due to a new feature being added. To begin with, this should be implemented using the github API, so only issues that are within github can be modified.

As time progresses, it's likely there will be more of these tickets, and we can support a consistent subset of operations to perform after a merge (e.g. perhaps a set of "git-risk hooks").

Start by reading the repository's Python entry point and its current merge and ticket analysis flow; the issue names no files or tests. Define the GitHub API operations and the criteria for an at-risk ticket before implementing the first GitHub-only workflow, with successful automatic marking and a clear post-merge result as the completion criteria.

Written by the indexing model from the issue text.