Enhancement : Plugin should specify which GitLab settings were changed and their new values after update

When using the GitLab plugin, if the user runs /gitlab settings notification or /gitlab settings reminders and changes the settings (on/off), the plugin only displays a message that the settings updated. Instead, it should specify exactly which settings were changed and their new values in the channel.

Start at the handlers for /gitlab settings notification and /gitlab settings reminders, then trace how the update confirmation is assembled. Done means the channel message identifies each changed setting and its new on/off value; verify both commands.

Written by the indexing model from the issue text.