Add headers to be able to track bidi usage (#6939)

Originally we were not tracking bidi usage in android. This PR enables
it by adding certain headers when the initial websocket connection is
made. There was some refractoring done wrt to extract out the part which
just adds the headers from the applyCommonConfiguration function

Author: VinayGuthal

firebase-ai/src/main/kotlin/com/google/firebase/ai/common/APIController.kt

@@ -164,7 +164,7 @@ internal constructor(
     "wss://firebasevertexai.googleapis.com/ws/google.firebase.vertexai.v1beta.LlmBidiService/BidiGenerateContent/locations/$location?key=$key"
 
   suspend fun getWebSocketSession(location: String): ClientWebSocketSession =
-    client.webSocketSession(getBidiEndpoint(location))
+    client.webSocketSession(getBidiEndpoint(location)) { applyCommonHeaders() }
 
   fun generateContentStream(
     request: GenerateContentRequest
@@ -191,12 +191,7 @@ internal constructor(
       throw FirebaseCommonAIException.from(e)
     }
 
-  private fun HttpRequestBuilder.applyCommonConfiguration(request: Request) {
-    when (request) {
-      is GenerateContentRequest -> setBody<GenerateContentRequest>(request)
-      is CountTokensRequest -> setBody<CountTokensRequest>(request)
-      is GenerateImageRequest -> setBody<GenerateImageRequest>(request)
-    }
+  private fun HttpRequestBuilder.applyCommonHeaders() {
     contentType(ContentType.Application.Json)
     header("x-goog-api-key", key)
     header("x-goog-api-client", apiClient)
@@ -205,6 +200,14 @@ internal constructor(
       header("X-Firebase-AppVersion", appVersion)
     }
   }
+  private fun HttpRequestBuilder.applyCommonConfiguration(request: Request) {
+    when (request) {
+      is GenerateContentRequest -> setBody<GenerateContentRequest>(request)
+      is CountTokensRequest -> setBody<CountTokensRequest>(request)
+      is GenerateImageRequest -> setBody<GenerateImageRequest>(request)
+    }
+    applyCommonHeaders()
+  }
 
   private suspend fun HttpRequestBuilder.applyHeaderProvider() {
     if (headerProvider != null) {