Add support for GitHub Apps

[Nicolas-M]

Is your feature request related to a problem? Please describe.
In GitHub, GitHub Apps are preferred over a user's token because they offer enhanced security, are more scalable, and do not consume a license seat. They also have built-in webhooks.

Describe the solution you'd like to see
Instead of a personal access token, I would like to provide Frogbot a GitHub App appID and privateKey.

Describe alternatives you've considered
I considered having a dedicated GitHub account for use with Frogbot, but this would take up a seat/license.

Additional context

• This feature would benefit both GHES and GitHub Cloud customers
• Comments and pull requests opened by a GitHub App are clearly marked as being made by a bot, which adds to their authenticity (see mockup below):

• Benefits of a GitHub App: https://docs.github.com/en/apps/creating-github-apps/about-creating-github-apps/deciding-when-to-build-a-github-app

[hadarshjfrog]

Hi @Nicolas-M - thanks for your suggestion!
Github App for Frogbot is currently in the works. Expected at Q3. Stay Tuned 🐸

cc: @orto17