www/caddy: Cleanup model, *.php and *.py files

[Monviech]

A general cleanup to remove unused code and check for consistency.

No functional changes.

• Model caddy.xml has been cleaned up of any keys that are default in their base fields.
• All php style warnings/errors have been fixed for PSR-12. make style
• Specifically, the certificate php extraction script has been split into two files, caddy_certs.php and run_caddy_certs.php to separate classes and side effects.
• rc.conf.d/caddy template has been refactored (that file was one of the first ever in the plugin)
• caddy_control.py and caddy_diagnostics.py have been refactored for PEP 8.