Allow Users to define Anti-Keywords.

### Your use case

I made the big mistake and my matrix server is contains my nickname jokergermany.XXX

#### What would you like to do?
Now i get a notification because "i got mentioned" when some of the ghost user on my matrix Server a mentioned.
It would be great if this could be stopped.

#### Why would you like to do it?
To get no notification when i am not mentioned.

#### How would you like to achieve it?
Allow Users to define Anti-Keywords.
e.g if someones matrix name is tim.
Allow him to define timcook as anti-keyword.

### Have you considered any alternatives?

Yes, there is another solution for MY Problem (#20518 ) , but i think this solution don't work for every problem like this

### Additional context

_No response_