Add some missing deprecation annotations

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/NamespacedKey.java

@@ -161,6 +161,7 @@ public final class NamespacedKey {
      */
     @ApiStatus.Internal
     @NotNull
+    @Deprecated
     public static NamespacedKey randomKey() {
         return new NamespacedKey(BUKKIT, UUID.randomUUID().toString());
     }