User manager: implement dummy group APIs

This is needed to unblock the SRCREV bump in
[1] https://gerrit.openbmc.org/c/openbmc/openbmc/+/58690

Tested:
the daemon compiles. Romolus QEMU testing also passed.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: I530dcb2e19b47872c985d8273bc41f7ff6d5d62d
diff --git a/user_mgr.hpp b/user_mgr.hpp
index e673527..3ba0012 100644
--- a/user_mgr.hpp
+++ b/user_mgr.hpp
@@ -323,6 +323,10 @@
     virtual void executeUserModifyUserEnable(const char* userName,
                                              bool enabled);
 
+    void createGroup(std::string groupName) override;
+
+    void deleteGroup(std::string groupName) override;
+
     virtual std::vector<std::string> getFailedAttempt(const char* userName);
 
     /** @brief check for valid privielge