Support user credentials login #28
Description
Currently only support generic connecting string, app reg or bearer tokens for authentication.
This is because main usage so far has been in pipelines, but there are obvious use cases to have a developer use the CLI locally (e.g. for plug reg and customisation generation etc.) so individual user authentication is required.
This isn't as straightforward as it used to be though, so careful consideration needs to be given on how it's implemented, interactive login, saving authentication profiles, MFA, etc.