Add release metadata to gitignore

Author: glibas

.gitignore

@@ -1,3 +1,10 @@
 .idea
 **/*.iml
-**/target/
+**/target/
+examples/pom.xml.releaseBackup
+pom.xml.releaseBackup
+release.properties
+scala/pom.xml.releaseBackup
+scala/scala_2.11/pom.xml.releaseBackup
+scala/scala_2.12/pom.xml.releaseBackup
+scala/scala_2.13/pom.xml.releaseBackup