Relying on git submodules for bot management

[skyborgff]

The use of submodules could possibly allow for an easier bot management. A git pull would only download the .submodules files, making it very quick, Assuming the use of folders to categorize bots, each category would have it's own submodules. A bot could fit multiple categories (like active and story-mode), and proper management (idk if git does this) could allow for a bot to only be downloaded once, even if in different folders. Having the list of bots on the first download would allow for bots to be downloaded on-demand by the user.

[skyborgff]

Could be used to preserve all bots that were done, and avoid trimming https://github.com/RLBot/RLBotPack/pull/310#pullrequestreview-1622003867