Consider making validate a prebuild step

[fishmonger45]

Currently with dummy chain types file a project will build correctly but the project will not be valid to run. We should consider running validation before building.

To reproduce:

1. Init a starter project
2. Add an invalid chaintypes file (eg json) to the project manifest
3. Build (yarn && yarn codegen && yarn build
4. Build should work fine but when running subql validate it will fail

Solution:
Add a prebuild script to package.json which runs node dependencies subql validate