make a public preview annotation for Imagen

Author: David Motsonashvili

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/FirebaseVertexAI.kt

@@ -22,6 +22,7 @@ import com.google.firebase.app
 import com.google.firebase.appcheck.interop.InteropAppCheckTokenProvider
 import com.google.firebase.auth.internal.InternalAuthProvider
 import com.google.firebase.inject.Provider
+import com.google.firebase.vertexai.common.PublicPreviewAPI
 import com.google.firebase.vertexai.type.Content
 import com.google.firebase.vertexai.type.GenerationConfig
 import com.google.firebase.vertexai.type.ImagenGenerationConfig
@@ -90,6 +91,7 @@ internal constructor(
    * @param requestOptions Configuration options for sending requests to the backend.
    * @return The initialized [ImagenModel] instance.
    */
+  @OptIn(PublicPreviewAPI::class)
   @JvmOverloads
   public fun imagenModel(
     modelName: String,

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/ImagenModel.kt

@@ -22,6 +22,7 @@ import com.google.firebase.vertexai.common.APIController
 import com.google.firebase.vertexai.common.AppCheckHeaderProvider
 import com.google.firebase.vertexai.common.ContentBlockedException
 import com.google.firebase.vertexai.common.GenerateImageRequest
+import com.google.firebase.vertexai.common.PublicPreviewAPI
 import com.google.firebase.vertexai.type.FirebaseVertexAIException
 import com.google.firebase.vertexai.type.ImagenGCSImage
 import com.google.firebase.vertexai.type.ImagenGenerationConfig
@@ -34,6 +35,7 @@ import com.google.firebase.vertexai.type.RequestOptions
  * Represents a generative model (like Imagen), capable of generating images based on various input
  * types.
  */
+@PublicPreviewAPI
 public class ImagenModel
 internal constructor(
   private val modelName: String,

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/common/PublicPreviewAPI.kt

@@ -0,0 +1,10 @@
+package com.google.firebase.vertexai.common
+
+@Retention(AnnotationRetention.BINARY)
+@RequiresOptIn(
+  level = RequiresOptIn.Level.ERROR,
+  message =
+    "This API is currently experimental and in public preview and may change in behavior in " +
+      "backwards-incompatible ways without notice.",
+)
+public annotation class PublicPreviewAPI()