fix: accept domain_verification intent for portal url generation

[adanselm]

Also upgrades hackney, fixes 1 warning and 5 tests.

[LauraBeatris]

Hey @adanselm, thanks for the contribution!

hackney is going to be removed on the major release, as we're going to use Tesla by default and allow for folks to use their HTTP client of preference #52

Also, we're removing those provider enum checks as it's the responsibility of the API to return a 400 error in case a client provides an invalid value.