caddy-gen refactor

[skyzh]

Caddyfile brings numerous issues for our site. We could leverage caddy JSON configuration scheme for better extensibility.

[skyzh]

Issues of Caddyfile:

• Do not support hot-reload. We need to restart our server every time.
• Brings bugs without notice. caddy-gen: fix logging #214
• Not cover full features of Caddy, and need special hacks. caddy-gen: fix missing http log #201