PostgreSQL migration

[builder-247]

Limitations of MongoDB:

• Querying nested json data is really slow - this caused custom leaderboards to break at around 80k players
• Since MongoDB stores key/value pairs, it takes a lot of storage space

PostgreSQL's JSONB format allows us to store the same data taking less space and being faster to query.

One big downside is that a lot of the API functionality has to be rewritten, for example a lot of filtering relies on MongoDB's query language.

Checklist moved to PR

[apollyon600]

Try saving all of the item data inside 1 object and then filter it when needed.
Instead of having separate data for each item if I'm reading this correctly.