feat: add tonic

Signed-off-by: kjuulh <contact@kjuulh.io>

crates/churn/proto/churn/v1/churn.proto

@@ -0,0 +1,25 @@
+syntax = "proto3";
+
+package churn.v1;
+
+service Churn {
+  rpc GetKey(GetKeyRequest) returns (GetKeyResponse);
+  rpc SetKey(SetKeyRequest) returns (SetKeyResponse);
+}
+
+message GetKeyRequest {
+  string namespace = 1;
+  optional string id = 2;
+  string key = 3;
+}
+message GetKeyResponse {
+  optional string value = 1;
+}
+
+message SetKeyRequest {
+  string namespace = 1;
+  optional string id = 2;
+  string key = 3;
+  string value = 4;
+}
+message SetKeyResponse {}