switch to httr2

[schochastics]

Eventually we should move to httr2 instead of relying on httr.

[chainsawriot]

The migration itself in the R directory should be straightforward. The difficult part would be the rewriting of many tests. But I agree that we should move to httr2; also take the opportunity to refactor some old code.

[schochastics]

Maybe also a chance to try out https://github.com/nealrichardson/httptest2? Have you used it before?

[Aariq]

vcr also works with most httr2 functions