signcolumn for preview windows (or more general window options)

[wookayin]

In function quickui#preview#display, we have some default window options set:

let cmdlist = ['setlocal signcolumn=no norelativenumber']

But I would want to have signcolumn enabled. I wish there were a configuration point for this (say opts.signcolumn).

More generally, a user may want to execute an arbitrary lines of vim commands to configure the preview window --- including many setlocal options, window highlights, custom keymappings, etc. What would be a suggested way for this?