Switch from httr to httr2

[pitkant]

httr package is marked in R lifecycle terms as superseded. This means generally speaking that

A softer alternative to deprecation is superseded. A superseded function has a known better alternative, but the function itself is not going away . A superseded function will not emit a warning (since there’s no risk if you keep using it), but the documentation will tell you what we recommend instead .

Superseded functions will not receive new features, but will receive any critical bug fixes needed to keep it working. In some ways a superseded function is actually safer than a stable function because it’s guaranteed never to change (for better or for worse).

and in the specific case of the httr package that

httr is superseded: only changes necessary to keep it on CRAN will be made.

I think it would make sense to update even existing functions from httr to httr2, since httr2 is more modern, is already used in e.g. the eurostat package and it is probably easier to maintain functions using httr2 in the future due to better documentation. Special care has to be taken to ensure that the returned data object is identical to the old one. Error message handling can differ from old implementation. Writing completely new functions in httr2 is also a no-brainer.

[pitkant]

Fixes to PR #24