refs https://github.com/TryGhost/Toolbox/issues/175
- we're going to be making some changes in v5 wrt supported databases
- we needed a way of detecting the difference between MySQL 5 + 8,
MariaDB etc
- I've created `@tryghost/database-info`, which is a small wrapper
around `knex`, which returns this information
- this commit:
- adds the library to Ghost
- initializes the DB info library upon boot
- updates the Admin API /config/ endpoint and UpdateCheck to return
the new string - `mysql5`, `mysql8` etc
