CAMEL-21461: platform-http - add CORS support

[rinaldodev]

Enable CORS support when using platform-http.

I'm unsure if this caching here could be an issue. Do we allow changing CORS configurations after initialization?

  if (corsConfiguration == null) {
      Map<String, String> corsHeaders = restConfiguration.getCorsHeaders();
      corsConfiguration = createCorsConfiguration(corsHeaders != null ? corsHeaders : Collections.emptyMap());
  }
  return corsConfiguration;

---

@Croway opening as draft to confirm if this is an issue. The following syntax doesn't work when testing CORS because it seems to overrides the behavior of all HTTP methods including OPTIONS. I don't think it's an issue since it's not the documented way of using rest DSL. Please confirm if you agree so I can remove the syntax from the test.

from("platform-http:/cors")
        .transform().constant("cors");

[Croway]

can you add a negative test please?
ala

            .when()
            .get("/rest")
            .then()
            .statusCode(4xx/5xx)
            ```

[Croway]

@rinaldodev The following syntax doesn't work when testing CORS because it seems to overrides the behavior of all HTTP methods including OPTIONS this sounds odd, what about using httpMethodRestrict? do you think this can help somehow?

[davsclaus]

Just a small thing, java source files should have ASF license headers.