Add option for marking a user as spammer in "Deactivate user" popover

Sometimes open communities have spammers sign up. Administrators can deactivate the spammer, but currently don’t have an easy way to clean up after them or annotate that the user is a spammer.

We should add spammer-specific functionality to the “Deactivate user” popover.

What to add:

1. At the bottom of the popover, a line that says: “Is this user a spammer?”, with a checkbox (unchecked by default).
2. If the checkbox is checked, the popover expands in the following way: a. A line that says: "Upon deactivation, this user will be renamed to “{username} (spammer).” b. A line that says: “What should be done with {user}'s messages?”, with a dropdown. Options: Nothing, Delete messages in public streams, Delete all messages. If one of the “Delete messages” options is selected, the user’s messages should be deleted as specified when the user is deactivated.

If the spammer checkbox is checked, the user should be automatically renamed as described above when the “Confirm” button is clicked.

Note that we should build this keeping in mind that we plan to extend the functionality for this widget in the future.

Related issues: #16473, #17100.

[alya]

@ligmitz @m-e-l-u-h-a-n FYI, since you expressed interest in #16473.

[madrix01]

@yogesh-sirsat I have made some progress with it. I was busy with other PRs, I will continue working on this PR soon.