[keyserver] Pass --performance-schema to MariaDB in docker-compose

Summary:
As I mentioned in D9304 it turns out we can totally just pass --performance-schema to mariadb. I was misled by some old MySQL (not MariaDB) docs as well as a comment someone left on GitHub that inaccurately stated that performance-schema had to be defined in a .cnf file and couldn't be passed as command line argument when started up. Annoying, but this is a much cleaner solution anyways.

Depends on D9304

Test Plan:
Confirmed that performance_schema was set as expected (docker-compose up):

Reviewers: ashoat, tomek, ginsu, rohan

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D9307