Add loading of mock scenarios

[charisk]

Adds a command to load a mock scenario for the mock GitHub API server to replay.

Checklist

N/A:

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[koesie10]

Looks good overall and a simple test worked.

My biggest concern is not being able to stop a scenario. Should we unload the request handlers when we start a new recording, and also have a command to unload them? I'm fine with implementing that in a follow-up PR as well.

[charisk]

My biggest concern is not being able to stop a scenario. Should we unload the request handlers when we start a new recording, and also have a command to unload them? I'm fine with implementing that in a follow-up PR as well.

Sorry I missed this on Friday. I've updated the current PR.