Allow dynamically change api version

[mikkohirvonen]

Hi

I want to update methods to use current v2 api version when available. I made some changes to library, see
https://github.com/mikkohirvonen/python-cert_manager/tree/dynamic-api-version/cert_manager

changes:
new method

• _endpoint:change_api_version

• update dcv.py to use v2 api on get_validation_status

is is something to committable?