fix: Define plug to install lemonade-server rather than the slot

Author: kenvandine

snap/snapcraft.yaml

@@ -108,7 +108,7 @@ plugs:
   shmem:
     interface: shared-memory
     private: true
-  foo-install-lemonade:
+  lemonade-server:
     interface: content
     content: foo
     target: $SNAP_DATA/foo