Allow to have multiple versions

Signed-off-by: Armel Soro <asoro@redhat.com>

Author: rm3l

stacks/java-maven/devfile.yaml stacks/java-maven/1.2.0/devfile.yamlstacks/java-maven/devfile.yaml renamed to stacks/java-maven/1.2.0/devfile.yaml

@@ -0,0 +1,7 @@
+name: java-maven
+description: 'Java application based on Maven and OpenJDK'
+displayName: Maven Java
+icon: https://raw.githubusercontent.com/devfile-samples/devfile-stack-icons/main/java-maven.jpg
+versions:
+  - version: 1.2.0
+    default: true # should have one and only one default version