Make release default branch

[Martinsos]

Thinking:

Vinny and I were just hitting some confusing issues with Codespaces because the button for them comes from default branch, but we really want them to use stuff from release which is not default, and seems we (well Vinny) solved it, but it prompted me to think about this a bit.

While we have a bit different names, we are actually following "git flow" approach it seems, where you have master which is the same thing as our release, then you have develop which is the same as our main, and you have feature branches which we also have.
I read in some places that it makes sense having master (so our release) as a default branch, because then when people come to the repo, they see stuff related to the latest version of your software, which is what they are likely interacting with -> not the bleeding edge (which is main aka develop). But it might cause some other issues hm, I am not sure. I am not sure if we are assuming somewhere that main is default.

@infomiho :

This makes sense to me

We linked to stuff on the release branch from the docs which makes sense. Using the same logic, release should be the default

I guess we would need to update the Github Action that builds stuff and couple of release related workflows / docs, but that's not so much?