[NO ISSUE][COMP] Issue a warning when a synonym was not created because it exists

- user model changes: no
- storage format changes: no
- interface changes: no

Details:
When creating a synonym with IF EXISTS, issue a warning when
the synonym was not created because it exists.

Change-Id: Iff9ec2f4e28db9824e93a4ab71dcfd85e716fec6
Reviewed-on: https://asterix-gerrit.ics.uci.edu/c/asterixdb/+/10463
Integration-Tests: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Ali Alsuliman <ali.al.solaiman@gmail.com>
Reviewed-by: Ian Maxon <imaxon@uci.edu>
diff --git a/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/translator/QueryTranslator.java b/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/translator/QueryTranslator.java
index 0a88832..64d0fd7 100644
--- a/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/translator/QueryTranslator.java
+++ b/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/translator/QueryTranslator.java
@@ -2664,6 +2664,10 @@
             if (synonym != null) {
                 if (css.getIfNotExists()) {
                     MetadataManager.INSTANCE.commitTransaction(mdTxnCtx);
+                    if (warningCollector.shouldWarn()) {
+                        warningCollector
+                                .warn(Warning.of(css.getSourceLocation(), ErrorCode.SYNONYM_EXISTS, synonymName));
+                    }
                     return;
                 }
                 throw new CompilationException(ErrorCode.SYNONYM_EXISTS, css.getSourceLocation(), synonymName);