Add samplesBranch property

Closes gh-10019

gradle.properties

@@ -4,6 +4,7 @@ springBootVersion=2.4.2
 openSamlVersion=3.4.6
 version=5.5.2-SNAPSHOT
 kotlinVersion=1.5.10
+samplesBranch=5.5.x
 org.gradle.jvmargs=-Xmx3g -XX:MaxPermSize=2048m -XX:+HeapDumpOnOutOfMemoryError
 org.gradle.parallel=true
 org.gradle.caching=true