Make auto_open option work nicely with manual toggling

[DanielCardonaRojas]

Hi @folke First of all thanks for this awesome plugin, I've been using this plugin for a while and recently enabled auto_open, I was trying to get an experience that would allow me to have early alerts but also found that auto_open would get in the way a bit reopening on each file save.

It would be nice if trouble.nvim would keep a count of lsp diagnostics per buffer or workspace so that when enabling auto_open = true you could still hide the trouble window and not having it reappear on each file save for example. If new issues appear in that case reopen automatically.