Previously, upstream URLs like 'https://iot2.fuo.fi' were passed directly
to Caddy's dial field, causing DNS lookup errors like 'lookup /iot2.fuo.fi'.
Changes:
- Parse upstream URLs to extract hostname:port for Caddy's dial field
- Automatically detect HTTPS upstreams and configure TLS transport
- Support insecure_skip_verify flag for self-signed certificates
- Default to port 443 for https://, port 80 for http://
Fixes: 'dial tcp: lookup /host: no such host' errors when using URL
format for upstreams instead of host:port format.
9354cd9407