Implement Gacha handling #12
Description
Gacha pulling along with % of each unit, specific configuration for it does not exist.
We already have the effects (https://github.com/decompfrontier/server/blob/main/deploy/system/gacha_effects.json) and each banner that was ever released (https://github.com/decompfrontier/server/blob/main/deploy/system/gacha.json) inside the server, but no logic exists to make use of this.
Perhaps it should also contain some configuration in the database about which things to enable and which not?
Some progress is already done in #7