added Action interface

server/src/main/java/keywhiz/service/permissions/Action.java

@@ -0,0 +1,23 @@
+package keywhiz.service.permissions;
+
+/**
+ * Action class defines the set of actions that can be performed on an object
+ * */
+public final class Action {
+  private Action() {}
+
+  // add clients to groups or add secrets to groups
+  public static final String ADD = "ADD";
+
+  public static final String CREATE = "CREATE";
+
+  // for secrets and permissions, it will be a soft deletion
+  public static final String DELETE = "DELETE";
+
+  public static final String READ = "READ";
+
+  // remove clients to groups or remove secrets to groups
+  public static final String REMOVE = "REMOVE";
+
+  public static final String UPDATE = "UPDATE";
+}