[Downloader] Repair repo function

[laggron42]

Feature request

Select the type of feature you are requesting:

• [ ] Cog
• [x] Command
• [x] API functionality

Describe your requested feature

I discussed a bit in #coding about a command in Downloader to repair broken repos. This may be related to the nukes recently dropped in my repo.

I'd gladly work on it, but I feel like we need to discuss about what it exactly does before I start coding. There are some questions that needs to be discussed, such as:

• Should the repair function simply remove and readd the repo? It could run other commands, there are plenty of commands made for repair (such as reset, prune, fsck, gc or reflog), not sure if it could be useful
• Should it attempt to repair cogs? If I take the example of my recently broken repo, people had to remove and readd the repo, then uninstall and install the codmw cog, other cogs were fine. How could the bot detect what cogs are broken and should be reinstalled?

[Jackenmen]

I'm freezing this for now as currently I do plan to support non-matching histories and if everything works out, this would not be needed.