fix: set request ID in tracing context key (#17602)

Since `addCustomerHeaders` middleware was after the `httpTracer`
middleware, the request ID was not set in the http tracing context. By
reordering these middleware functions, the request ID header becomes
available. We also avoid setting the tracing context key again in
`newContext`.

Bonus: All middleware functions are renamed with a "Middleware" suffix
to avoid confusion with http Handler functions.

cmd/crossdomain-xml-handler.go

@@ -30,7 +30,7 @@ const crossDomainXMLEntity = "/crossdomain.xml"
 // When clients request content hosted on a particular source domain and that content make requests
 // directed towards a domain other than its own, the remote domain needs to host a cross-domain
 // policy file that grants access to the source domain, allowing the client to continue the transaction.
-func setCrossDomainPolicy(h http.Handler) http.Handler {
+func setCrossDomainPolicyMiddleware(h http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		// Look for 'crossdomain.xml' in the incoming request.
 		if r.URL.Path == crossDomainXMLEntity {