Create .env.example (#562)

* Create .env.example

.env.example file with required env variables not added hence adding

* Rename .env.example to env.example

file name corrected as directed

examples/websocket-server/env.example

@@ -0,0 +1,8 @@
+# OpenAI API Key
+OPENAI_API_KEY=your_openai_api_key_here
+
+# Deepgram API Key
+DEEPGRAM_API_KEY=your_deepgram_api_key_here
+
+# Cartesia API Key
+CARTESIA_API_KEY=your_cartesia_api_key_here