Add hook utility basic implementation

vars/hook.groovy

@@ -0,0 +1,15 @@
+def call(String name) {
+    def rootDir = pwd()
+    def filepath = "${rootDir}/.jenkins/${name}.groovy"
+    def exists = fileExists(filepath)
+    if (!exists) {
+        println("No hook '${filepath}' script. Skipping.")
+        return
+    }
+    def hook = load(filepath)
+    if(hook.metaClass.respondsTo(hook, 'exec')) {
+        hook.exec()
+    } else {
+        error("Hook script '${filepath}' exists but does not expose an exec() function.")
+    }
+}