Add support for OFF

Author: daymxn

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/HarmBlockThreshold.kt

@@ -25,6 +25,7 @@ public class HarmBlockThreshold private constructor(public val ordinal: Int) {
 
   internal fun toInternal() =
     when (this) {
+      OFF -> Internal.OFF
       NONE -> Internal.BLOCK_NONE
       ONLY_HIGH -> Internal.BLOCK_ONLY_HIGH
       MEDIUM_AND_ABOVE -> Internal.BLOCK_MEDIUM_AND_ABOVE
@@ -39,6 +40,7 @@ public class HarmBlockThreshold private constructor(public val ordinal: Int) {
     BLOCK_MEDIUM_AND_ABOVE,
     BLOCK_ONLY_HIGH,
     BLOCK_NONE,
+    OFF
   }
 
   public companion object {
@@ -53,5 +55,13 @@ public class HarmBlockThreshold private constructor(public val ordinal: Int) {
 
     /** All content is allowed regardless of harm. */
     @JvmField public val NONE: HarmBlockThreshold = HarmBlockThreshold(3)
+
+    /**
+     * All content is allowed regardless of harm.
+     *
+     * The same as [NONE], but metadata when the corresponding [HarmCategory] occurs will **NOT** be
+     * present in the response.
+     */
+    @JvmField public val OFF: HarmBlockThreshold = HarmBlockThreshold(4)
   }
 }