🛠 Change setup tooling to use `yarn setup` (#9413)
🛠 Change setup tooling to use `yarn setup` (#9413)

no issue

1. renamed alias:
  - we have a special alias that does initial setup tasks that are only supposed to be run once
  - changing the alias to be `setup` rather than `init` otherwise it is too easy to confuse with `grunt init`
2. require globals to be installed manually
  - yarn is RUBBISH at managing globals
  - internally we use npm for this (actually we have a managed list of globals) and yarn for everything else
  - by moving this to documentation, rather than a command, we have flexibility to do this differently
  - also explicit globals are better than installing these without the user knowing IMO
3. setup includes knex-migrator
  - do this automatically instead of knex-migrator init being a separate command
  - every other time knex-migrator is needed, Ghost _should_ tell you what to do
dbalders/Ghost,kevinansfield/Ghost,e10/Ghost,TryGhost/Ghost,acburdine/Ghost,kevinansfield/Ghost,ErisDS/Ghost,bitjson/Ghost,janvt/Ghost,kevinansfield/Ghost,Gargol/Ghost,acburdine/Ghost,chevex/undoctrinate,dbalders/Ghost,Kikobeats/Ghost,Gargol/Ghost,ErisDS/Ghost,ErisDS/Ghost,JohnONolan/Ghost,JohnONolan/Ghost,bitjson/Ghost,dbalders/Ghost,acburdine/Ghost,e10/Ghost,Kikobeats/Ghost,janvt/Ghost,JohnONolan/Ghost,TryGhost/Ghost,Kikobeats/Ghost,TryGhost/Ghost