security/py-certbot: Improve periodic script

This change will keep the default behavior in the periodic script
and will add options to customize each parameter for those who want to:

• weekly_certbot_pre_hook
• weekly_certbot_post_hook
• weekly_certbot_deploy_hook
• weekly_certbot_custom_args

PR: 245674, 245954
Reported by: amdmi3, fjoe
Reviewed by: koobs
Approved by: dbaio, koobs (python, maintainer)
MFH: 2020Q3
Differential Revision: https://reviews.freebsd.org/D25391