Summary: Add license checker and linter. Will add the license separately, to prevent noise in review.

Test Plan: Tested on several license variants.

Reviewers: vihang, michelle

Reviewed By: michelle

JIRA Issues: PP-2566

Differential Revision: https://phab.corp.pixielabs.ai/D8240

GitOrigin-RevId: ab8509355d4bcd23f9ec3557f4a425ee4d49e1c0