Add sync and test global scripts

[IlCallo]

We need to make some test-project related scripts available at repo-wide level, eg. "sync:all" or "test:all"

We could rely on Lerna for this as it's already there, but I never actually took the time to check how to use it properly
Internal-documentation-wise, the testing repo was in a pretty bad shape when I took responsability for it a while back, I tried to upgrade lerna at some point but only got headaches and stopped there

Also, Lerna has been unmaintained for quite some time now and only recently NX guys offered themselves to maintain the project