Self-Publishing an eBook as a Developer

I recently turned an old article into an eBook as a few people had asked me for an offline copy, and found the process of actually doing it fairly interesting and complicated. I couldn't find many retrospective posts about actually self-publishing something like this, especially not from the perspective of a developer wanting to just publish something they've already written, so I wrote about it in case anyone finds it interesting or wants to give it a go themselves.