feat: mariadb connection pooling
feat: mariadb connection pooling

Start initial pool of 4 (_POOL_SIZE) connections for a given site. When
the pool is exhausted, generate new connections upon request and add
them to the pool. Max allowed size for each pool is 64 (_MAX_POOL_SIZE)
connections. However, you may have more than 64 active connections, just
that they won't be pooled but destroyed upon job completion/end of
request/similar cycle.

frappe/frappe,StrellaGroup/frappe,StrellaGroup/frappe,StrellaGroup/frappe,frappe/frappe,frappe/frappe