Set user as Busy in GitHub when status in Mattermost is OOO

[hanzei]

When a user gets itself as OOO in Mattermost, the plugin should also set the user as Busy in GitHub (and revert the change once the user is back in office).

This might required changes to the plugin hooks.

[akshat-khosya]

I would like to work on it.

[hanzei]

Thanks @akshat-khosya 👍