[terraform] MariaDB RDS config options

Summary:
This sets mostly the same parameter options as MariaDB besides innodb_buffer_pool_size which is set to {DBInstanceClassMemory*3/4} matching our phabricator database and general recommendations.

Here are the configuration options in our keyserver docker compose file:

--performance-schema
--max-allowed-packet=256M
--local-infile=0
--sql-mode=STRICT_ALL_TABLES
--innodb-buffer-pool-size=1600M
--innodb-ft-min-token-size=1
--innodb-ft-enable-stopword=0

Test Plan: successful terraform deploy. Ran transfer process and successfully accessed the rds instance with mysql

Reviewers: ashoat, bartek, varun

Reviewed By: bartek

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D12322