sip_proxy: add SIP context to TRA requests (#22022)

This PR contains the following changes:

* SIP Proxy extension TRA API updated to send additional SIP context (method type and from header), so TRA service can use this information for customized affinity management.
* Fix an error with decoding of SIP headers with a valid format causing Envoy proxy to crash in case of empty header fields.

Risk Level: Low
Testing: Unit tests
Docs Changes: None
Release Notes: None
Platform Specific Features: None
Signed-off-by: Jonah Murphy <jonamurp@cisco.com>
Signed-off-by: Adrian Rejas Conde <arejasco@cisco.com>

Mirrored from https://github.com/envoyproxy/envoy @ 09549da9045d9c85ffaf851b6d740de0b507708f

contrib/envoy/extensions/filters/network/sip_proxy/tra/v3alpha/tra.proto

@@ -90,6 +90,8 @@ message TraServiceResponse {
 
 message CreateRequest {
   map<string, string> data = 1;
+
+  map<string, string> context = 2;
 }
 
 message CreateResponse {
@@ -97,6 +99,8 @@ message CreateResponse {
 
 message UpdateRequest {
   map<string, string> data = 1;
+
+  map<string, string> context = 2;
 }
 
 message UpdateResponse {
@@ -104,6 +108,8 @@ message UpdateResponse {
 
 message RetrieveRequest {
   string key = 1;
+
+  map<string, string> context = 2;
 }
 
 message RetrieveResponse {
@@ -112,6 +118,8 @@ message RetrieveResponse {
 
 message DeleteRequest {
   string key = 1;
+
+  map<string, string> context = 2;
 }
 
 message DeleteResponse {