Make releases dropdown form method GET instead of POST

[GregKaleka]

On the /releases/ page, the version dropdown form performs a POST request, which is a bit silly. We should change this form to perform a GET request.

[sdarwin]

On this point, just to clarify, Django automatically adds a csrf_token to forms with method="POST". If we change it to GET, then new users will not see the csrf token in the first place. That obviously won't remove cookies for users who visited the site before such a change.

That is probably often the case. And it's a very good point!

At the same time... I was able to remove the csrf_token from a few pages (including the one under discussion, I believe.) See https://github.com/boostorg/website-v2/pull/1073/files . So that issue should be solved.

if switching from POST to GET doesn't cause the URL in the browser bar to add many extra variables.... then this update could still be done