Caddy directive/variable for Reverb proxy

[fouteox]

The Problem

Laravel Reverb requires requests to /app/* and /apps/* to be reverse-proxied to the Reverb container.

The existing CADDY_SERVER_EXTRA_DIRECTIVES environment variable cannot be used for this because it's positioned after php_server in the Caddyfile.

The following code must be placed BEFORE the root directive in the Caddyfile. This could be done with an environment variable, like REVERB_PROXY or REVERB_CONTAINER.
The advantage is that it avoids us having a subdomain exclusively for Reverb.

@reverb { path /app/* /apps/* } handle @reverb { reverse_proxy reverb:8080 }