This is a follow-up from {T218265}.
=== Value proposition
We should support muting notifications for users from //Special:Mute//, which is the special page we will be using for {T218270} and {T218266}. This is also a step forward towards bringing the mute lists closer.
=== Acceptance criteria:
* Add the second checkbox (//Mute notifications from this user//) on Special:Mute page:
{F28582602, width=400}
* If a user checks this checkbox and hits save, the user they are muting is added to the //Muted users// list under the //Notifications// tab in Special:Preferences.
* After save, the checkboxes and //Mute user// button go away and a confirmation message displays: //User:ABC has been muted. See all muted users in [Special:Preferences](https://en.wikipedia.org/wiki/Special:Preferences)//. - the link goes to Special:Preferences on the wiki they are on.
* If a user lands on //Special:Mute// with the user they request to mute already being in one or both of the mute lists, those respective checkboxes are already checked. Unchecking a box and saving the form, removes the user from the respective mute list.