FR: `jj untrack --local`, `jj untrack --ignore`

[lf-]

Is your feature request related to a problem? Please describe.
I want to be able to easily untrack a file and have it stick without having to manually edit a gitignore/.git/info/exclude file. This could be achieved by automatically editing the relevant gitignore file (probably the nearest one to the file for --ignore?) to add the file, and for --local, .git/info/exclude.

Describe the solution you'd like
jj untrack could be taught how to make untracking sticky, and print a warning if the file will get immediately tracked again suggesting the command that sticks the untracking.

Describe alternatives you've considered

Status quo: have to open an editor/type another command to do the untracking operation.
Reduce the necessity for untracking things (see #323).

Additional context
Add any other context or screenshots about the feature request here.

[ParadaCarleton]

This could be achieved by automatically editing the relevant gitignore file (probably the nearest one to the file for --ignore?) to add the file, and for --local, .git/info/exclude.

Just a comment: this could be done a lot more easily if we had some kind of .jj-ignore file supporting jj's fileset syntax. In that case, jj untrack $FILESET is trivial (it just writes $FILESET to the .jj-ignore).

I think this approach of combining the concepts of file tracking and ignoring plays very nicely jj's philosophy of eliminating unnecessary complexity and statefulness from git (like the staging area).

[PhilipMetzger]

Just a comment: this could be done a lot more easily if we had some kind of .jj-ignore file supporting jj's fileset syntax. In that case, jj untrack $FILESET is trivial (it just writes $FILESET to the .jj-ignore).

See #3525 for that specific issue.