Add comment about Kotlin 2.0

Author: seratch

pom.xml

@@ -51,6 +51,8 @@
         <jakarta.servlet-api.version>5.0.0</jakarta.servlet-api.version>
         <okhttp.version>4.12.0</okhttp.version>
         <gson.version>2.11.0</gson.version>
+        <!-- Upgrading to 2.0 for building this SDK modules should be safe enough,
+          but we'll hold off the upgrade for a few weeks, just in case. -->
         <kotlin.version>1.9.24</kotlin.version>
         <!-- Allow use by clients on earlier versions of Kotlin-->
         <kotlin.compiler.apiVersion>1.6</kotlin.compiler.apiVersion>