Adding router proxy support

[cx-serhii-stanislavskyi]

Add Router Proxy Configuration from Environment Variables

This PR adds two new functions to improve router connectivity options:

Changes

1. Added routerProxyFromEnvironment function

   • Enables automatic proxy configuration for router connections based on environment variables
   • Uses HTTPS_PROXY or HTTP_PROXY environment variables to determine proxy settings
   • Automatically applied when loading configuration from file via NewConfigFromFile()

2. Added parseTLS(raw string) helper function

   • Supports router URLs with the format tls:router.example.com:443
   • Converts tls: scheme URLs to proper HTTPS URLs for processing
   • Enables more flexible router addressing options

Use Cases

• Simplifies deployment in environments where direct connections are restricted and proxies are required
• Allows for consistent proxy configuration across applications using environment variables
• Supports more intuitive TLS connection specification with the tls: URL format

These changes maintain backward compatibility while adding flexibility for different network configurations.

[plorenz]

Apologies for the late review.

First, if you haven't yet, please take a look at https://github.com/openziti/sdk-golang/blob/main/CONTRIBUTING.md as a CLA is required for contributors.

Second, overall looks good. I'd like this function to be available to SDK users, but not have it set on RouterProxy by default. To that end, could you remove the set and make the method public?

[cx-serhii-stanislavskyi]

My apologies for the late response.

1. We're still clarifying question with CLA with legal team.
2. I made this method public, but I'm not sure how to implement it in zrok.
   We're expecting the routerProxy configuration here:
   https://github.com/openziti/sdk-golang/blob/main/ziti/ziti.go#L1461

    if context.routerProxy != nil {
		if proxyConfig := context.routerProxy(ingressUrl); proxyConfig != nil {
			dialerConfig.TransportConfig[transport.KeyCachedProxyConfiguration] = proxyConfig
		}
	}

That's inside connectEdgeRouter method.
It's for passing proxy configuration to edge router when we're creating public share

[plorenz]

See comment