Change main branch version to 2.12.0-SNAPSHOT (opensearch-project#5637)

Signed-off-by: Krishna Kondaka <krishkdk@amazon.com>

Author: kkondaka

gradle.properties

@@ -5,5 +5,5 @@
 
 # ATTENTION: If you are changing the version, please change the DataPrepperVersion whenever the major or minor version changes.
 # See: https://github.com/opensearch-project/data-prepper/blob/main/data-prepper-api/src/main/java/org/opensearch/dataprepper/model/configuration/DataPrepperVersion.java#L9
-version=2.11.0-SNAPSHOT
+version=2.12.0-SNAPSHOT
 org.gradle.jvmargs=-Xmx2048M