Add a "require" list

[abscondment]

This seems like a natural extension to the current allowlist and denylist implementation.

Use cases I've encountered recently: ensure every main package in this project imports...

• "go.uber.org/automaxprocs" to adjust GOMAXPROCS based on CPU quota (link)
• "crypto/tls/fipsonly" to force tls into FIPS mode at build time (link)

I'm sure other folks will find other uses.