Restrict channel aliases to 19.03

[tianon]

This will remove the "test" and "stable" aliases for whatever major release comes after 19.03 (so once the next release comes out, "stable" will become a stale alias).

I'm not 100% sure this is the right answer, but the "stable" alias has definitely been a huge source of confusion very recently (and it doesn't have much meaning anymore anyways given the death of the "edge" channel).

Closes #178

[tianon]

@thaJeztah would you mind sharing any thoughts you might have on this? 🙏 ❤️

[thaJeztah]

hm, right, so isn't the confusion only there at moments when there's no beta/rc?

If there's a beta available, then test and stable are different.

I agree that "stable" has lost some of its meaning with "edge" no longer being a thing (just wondering if it'll break people); perhaps we should also look at stats, and see how popular the various tag permutations are

[tianon]

The confusion I've seen recently has entirely been around the word stable -- believing it to somehow mean the tag will never change, or something? Or that it will somehow be immune to backwards incompatibility? I don't pretend to understand the full depth of the confusion, but I do understand the sentiment that stable isn't necessary a "stable" tag (and that it's really just the latest release of Docker, which is exactly what latest is/means).

I don't have any access to per-tag stats (and have been told that's not something we can realistically get), but if you've got them that would certainly be helpful. 😅

[tianon]

FWIW, the "breaking people" argument is why I think we should leave it around for 19.03, and once whatever's next comes out and 19.03 is no longer considered the latest "stable", the tag will simply drop away naturally (and become a stale "unsupported" tag).

[tianon]

More cases of folks seeming to misunderstand what is meant by the "stable" tag: #240 😞