Config option to allow a custom project completion update filter

[yongli-abc]

Currently, when updating the auto-completion project lists, it's either using the projects of the currently shown tasks, or using the projects from all tasks (including completed tasks). https://github.com/kdheepak/taskwarrior-tui/blob/main/src/app.rs#L3616-L3620

However, projects completed long time ago might be irrelevant now. Personally I would love to only see projects from currently pending tasks.

A more flexible approach is to allow configuring a default filter option, using which to load the projects for auto-completion. This would also enable the use case as "I'd like to only see projects during the past X months".