Add GIT support via UI for configuration management

**Describe the problem you have/What new integration you would like**
The ability to specify a upstream git repository for managing configuration versioning.

**Please describe your use case for this integration and alternatives you've tried:**
Currently, the workaround is to manually initialize a git repository in the esphome data directory, and to either manually trigger a git add/git push after updates are performed, or to setup a cron job to invoke a script to check in changes to a git repository.

Ideally- this proposed feature, would enable some basic git integration, to automatically push changes to a upstream git repository. As a future goal, the ability to see previous version directly via the esphome UI would be nice too.

**Additional context**

No files, tests, or entry points are named. Start by locating the existing ESPHome configuration-management UI and the data-directory workflow, then determine the scope for specifying an upstream Git repository and automatically pushing updates; done should include documented repository configuration and reliable push behavior.

Written by the indexing model from the issue text.