Fix platform-http-proxy example: reverse proxy instead of self-referential CamelHttpUrl

[Croway]

Summary

The platform-http-proxy example was broken in three ways:

• The README's curl --proxy command never reached the route: servlet containers normalize an absolute-form request line down to just the path, discarding the target host, so the request never matched platform-http:proxy/*.
• toD("${headers.CamelHttpUrl}") used the incoming request's own URL (CamelHttpUrl is set from request.getRequestURL(), i.e. this application's own address), causing the route to call itself in an infinite loop until the HTTP connection pool exhausted (503s).
• The consumer path literal proxy collides with a reserved marker in camel-platform-http that turns the endpoint into a catch-all consumer for a Host-header-based forward proxy - a mode only implemented by the Vert.x platform-http engine, not by camel-platform-http-starter (the servlet/Spring MVC engine this example uses). Left as-is it silently degrades into an unguarded catch-all matching unrelated paths instead of 404ing.

Redesigned as a real path-based reverse proxy: requests under /reverse-proxy/** are forwarded to a configurable backend (reverse-proxy.target-base-uri) using camel-http's bridgeEndpoint mode, which appends CamelHttpPath/CamelHttpQuery onto the fixed target automatically instead of trusting a self-referential header.

Test plan

• mvn compile on the module
• Ran the app locally and hit it with curl against real httpbin.org:
  • GET /reverse-proxy/get?arg1=val1 forwards to httpbin.org/get, query string preserved
  • GET /reverse-proxy and /reverse-proxy/ forward correctly to the backend root
  • Unrelated paths (/nope, /xyz, /reverse-proxyfoo, /other/path) correctly return 404 instead of being swallowed by the route (this used to silently catch-all under the old proxy literal path)