Improved threading performance on non-SQLite clients
Improved threading performance on non-SQLite clients

refs https://github.com/TryGhost/Ghost/pull/12431

- child_process are more expensive to run comparing to worker_threads (ref. https://wanago.io/2019/05/20/node-js-typescript-14-performance-hooks/)
- limiting child process only to sqlite backed instances allows high load servers running with MySQL (most usecases) to continue using worker_threads

bitjson/Ghost,TryGhost/Ghost,TryGhost/Ghost,ErisDS/Ghost,janvt/Ghost,e10/Ghost,ErisDS/Ghost,TryGhost/Ghost,bitjson/Ghost,e10/Ghost,janvt/Ghost,ErisDS/Ghost