Allow footgun prompts to also override customInstructions

[RSO]

A user reached out through our support inbox, explaining that they were surprised to find out that footgun prompting still includes customInstructions like .kilocode/rules and memory-bank. While I can definitely see why this was built in the way that it was, maybe it would make sense if we offer users a way to disable the inclusion of customInstructions? Like, we could change the footgun prompt to be a template, so that the user can decide whether they wish to include ${customInstructions} or not.

What do you think?