HTTP DELETE to delete a participant session - relay signal message for (#1143)

* HTTP DELETE to delete a participant session - relay signal message for
that.

Also, doing a basic signal cache and building server message and client
message cache on top of it.

* generated protobuf

---------

Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

Author: boks1971

protobufs/rpc/signalv2.proto

@@ -18,6 +18,7 @@ package rpc;
 
 option go_package = "github.com/livekit/protocol/rpc";
 
+import "google/protobuf/empty.proto";
 import "options.proto";
 import "rpc/signalv2_types.proto";
 
@@ -48,4 +49,15 @@ service Signalv2Participant {
       };
     };
   }
+
+  rpc RelaySignalv2ParticipantDeleteSession(RelaySignalv2ParticipantDeleteSessionRequest) returns (google.protobuf.Empty) {
+    option (psrpc.options) = {
+      topics: true
+      topic_params: {
+        group: "common"
+        names: ["topic"]
+        typed: true
+      };
+    };
+  }
 }

protobufs/rpc/signalv2_types.proto

@@ -42,3 +42,9 @@ message RelaySignalv2ParticipantRequest {
 message RelaySignalv2ParticipantResponse {
   livekit.Signalv2WireMessage wire_message = 1;
 }
+
+message RelaySignalv2ParticipantDeleteSessionRequest {
+  string room = 1;
+  string participant_identity = 2;
+  string participant_id = 3;
+}