feat: option to combine completion.list.selection = "auto_insert" and "preselect"

[SamuelBorn]

Feature Description

Citation from default config:

-- 'preselect' will automatically select the first item in the completion list

-- 'auto_insert' will not select any item by default, and insert the completion items automatically when selecting them

I would like to the see another option that combines them both. The documentation could be described as:

-- 'preselect_auto_insert' will automatically select the first item in the completion list, and insert the completion items automatically when selecting them

The default preselect action though should not trigger auto_insert as this would be annoying.

So to accept the first solution one still has to press the keyboard shortcut for accept or select_and_accept.

But after selecting with select_prev and select_next, auto_insert should trigger and accepting would no longer be necessary.