update salt size (#15758)

As part of becoming FIPS compliance, we are seeing this error: salt must be at least 128 bits when we run the Druid code against FIPS Compliant cryptographic security providers.
This PR fixes the salt size used in Pac4jSessionStore.java

extensions-core/druid-pac4j/src/main/java/org/apache/druid/security/pac4j/Pac4jSessionStore.java

@@ -65,7 +65,7 @@ public class Pac4jSessionStore<T extends WebContext> implements SessionStore<T>
         "CBC",
         "PKCS5Padding",
         "PBKDF2WithHmacSHA256",
-        8,
+        128,
         65536,
         128
     );