feat: add topic poc

.gitignore

@@ -3,3 +3,4 @@
 .phpunit.result.cache
 .idea/
 .vscode/
+.DS_Store

composer.json

@@ -22,6 +22,7 @@
             "Momento\\": "src/",
             "Cache_client\\": "types/Cache_client/",
             "Control_client\\": "types/Control_client/",
+            "PubsubClient\\": "types/Cache_client/Pubsub",
             "Auth\\": "types/Auth/",
             "GPBMetadata\\": "types/GPBMetadata"
         },
@@ -45,7 +46,8 @@
         "google/protobuf": "3.22.3",
         "grpc/grpc": "1.52.0",
         "psr/log": "^1.1 || ^2.0 || ^3.0",
-        "psr/simple-cache": "^1.0.1 || ^3.0"
+        "psr/simple-cache": "^1.0.1 || ^3.0",
+        "ext-json": "*"
     },
     "require-dev": {
         "composer/composer": "^2.4.1",