Add option to disable auto completion for commands

[aabiji]

Don't draw the auto completion box that appears
when typing : when prompt-completion = true.

[nik-rev]

I'm curious why someone would want this. Do you memorise every typable command? More importantly, do you not need the automatic completion and the ability to tab through the commands?

Helix generally doesn't add config options if it can go without them. this is one of the places where I think a config option isn't needed

[aabiji]

You can use tab to autocomplete a command and cycle through the commands. That still works, the autocomplete box is just not shown.
Also, it's somewhat annoying and distracting to have the autocompletion box flash when quickly entering commands, like when saving for example. So I think a configuration option is needed. It could be enabled by default, but the option should always be there to disable it if you want.