People lint: add ignore role warnings option

[jessemortenson]

Adds a --ignore-role-warnings flag to the people lint command that avoids displaying warnings about active roles. Continues to emit errors, so this is really just about reducing verbosity around the muni/executive people.

[fishdan]

Looks good to me. The new flag is threaded from the people lint CLI into Validator and only suppresses the intended municipal/executive “no active roles” warning path; role errors still remain errors.

One small follow-up I’d consider: add a direct unit test for ignore_role_warnings=True on a municipal or executive person with no active roles, so the new behavior is locked in rather than only covered through argument plumbing. Not a blocker.

I checked the PR build and it is passing.