feat: automatic validator version fetching

[baarthur]

Hey guys,

I am proposing a few changes to how download_validator() works. Instead of relying on a hardcoded vector of versions, this version fetches the latest version automatically. The main difference is in the helper function get_validator_url(). As a downside, this adds httr2 to the list of dependencies, which I believe is a minor nuisance since httr2 is widely adopted and the gains in automation are high, by eliminating the need to manually update the list of versions.

I also provided an optional list_validator_versions(), which returns a df with the available CLI versions and their URLs. But honestly, I believe it is overkill, i.e., a user who wishes to use a later version probably knows it beforehand; otherwise, they may not have a strong reason to use, say, v5.0.0 instead of v7.0.0. It could also be used instead of get_validator_url(), but I think the former works just fine, as list_validator_versions() uses an API which is limited to 60 requests before authentication.

Closes #86.

[rafapereirabr]

this looks like a good suggestion that makes package maintenance much easier. The checks are failling for a few OSs , though.

[baarthur]

the problem seems to be with java. it seems that I need to update the actions workflow to include the latest java and distro. be back in a few

[baarthur]

Done. For the record, the main issue is that the new canonical validator requires java 17, whereas our checks were using java 11.