Allow filtering by user/process by default

[sabarish-vm]

Checklist

• I've looked through the documentation and existing open issues for similar feature requests.

Describe the feature request

It would be nice to have the processes panel to show only the processes run by a user by running something "btm -u" directly from the shell, an existing example would be "htop -u". It feels like a bit of work at the moment to filter the processes panel by typing "user " every time. Maybe this could also be extended for filtering processes by command names, an existing example would be "htop -F ".

Both of these are especially beneficial if one is using bottom on a computing cluster.

[ClementTsang]

Updated the title to better match your request, but this might be a duplicate of #405.