Summary:
This uses the yaml to figure out what certs to renew instead of relying
on a cert dir locally. Also some additional cleanup to make this script easier
to grok.

Test Plan: Ran the renewal and cert creation scripts.

Reviewers: michelle, philkuz

Reviewed By: michelle
Signed-off-by: Vihang Mehta <vihang@pixielabs.ai>

Differential Revision: https://phab.corp.pixielabs.ai/D9983

GitOrigin-RevId: 1899f83f2d6b80e9f3b3ca2e1eafab67dae8bd6a