Support container registries using Basic Auth

[benwaffle]

What this PR does / why we need it:
Some container registries use just Basic auth to fetch images, instead of the Bearer token flow

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):

Please check the following list:

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[liulanzheng]

LGTM

[liulanzheng]

@benwaffle Would it be possible to also implement this feature in registryfs v1？

[benwaffle]

@liulanzheng sorry, I don't have the time to work on that right now

[liulanzheng]

@benwaffle ok，let's not support v1 for now, and we can add it later. I will complete it when I have time, and it would be even better if you have time to do it as well.