feature: Add a `!stats` command for stats on Python discord repos

[DragonSenseiGuy]

Adding a !stats command with the arguments of <timestamp_start, <timestamp_end> and <repo>.
Example response:

Stats for the bot repository:
Issues opened: 20
Issues closed: 15
Pull Requests opened: 10
Pull Requests closed: 2
Pull Requests merged: 8
Stars gained: 100
New contributors: 10
Commits:50

We can always add more statistics if needed or add more arguments to control the statistics.
This would also work for other repositories like Sir Lancebot, Pythondiscord Site, Snekbox, Sir Arthur and Metricity