Update for Caddy 2

[mholt]

Caddy 2:

• uses IANA identifiers for cipher suites: https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml
• uses TLS 1.2-1.3 by default
• does not require a path matcher to match all requests

Caddy 2 tls docs: https://caddyserver.com/docs/caddyfile/directives/tls and header directive examples: https://caddyserver.com/docs/caddyfile/directives/header#examples

Feel free to double-check my work. I made this change at midnight. 😅

[april]

Closed, since this was resolved with a different PR. :)