Create CODE_OF_CONDUCT.md: a political tool to refer to prior following its rules and guidelines

Nobody has claimed this yet.

#1719 initial commit was such an attempt. Recent events under Heads matrix channel, where multiple usernames having the same writing style, asking irrelevent questions over days and not respecting many of its channel requests to use threads, and stay focus on topic now justifies revisiting and creating such code of conduct file to refer to.

Today was the fist banning of such user. I acted with patience with all past occurences of what appears to be trolling, while old usernames are replaced by newer usernames and I have no personal experience dealing with trolling. My intuition is that banning one will make two come. Unfortunately, the channel has only two moderators and only one of them is active: me. So not sure how to deal with this in a sustainable way, so this issue is an attempt to track pervious and now current suggestions, which I will organize on this OP post after discussions with the community. Expect multiple editions.

Some history:
- #1719 was initially introducing a code of conduct, but received pushbacks.
- Such CODE_OF_CONDUCT was removed from #1719 in commit https://github.com/linuxboot/heads/commit/fb4bdc0ce223039bcbffe51c1d8af53d9fe99e7e, where the the deleted content can be read at https://github.com/linuxboot/heads/blob/138a41db179e8e11b542a7ddf47b120dcacfd536/CODE_OF_CONDUCT.md

Review issue #1719 and the deleted CODE_OF_CONDUCT.md from commit fb4bdc0ce223039bcbffe51c1d8af53d9fe99e7e. Follow the discussion and prior suggestions before drafting; this is done when the community agrees on the content and a CODE_OF_CONDUCT.md is added.

Written by the indexing model from the issue text.