Make utility registry require credentials

[RothAndrew]

At the very least, the utility registry should require credentials to push images. Ideally these creds would be dynamically handled similarly to #3.

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Migrated from https://repo1.dso.mil/platform-one/big-bang/apps/product-tools/zarf/-/issues/9

[jeff-mccoy]

@RothAndrew this would be a good high value task you could do without code changes I think

[jeff-mccoy]

@RothAndrew moved this up in the roadmap because I feel it's a pretty important / lacking component for Zarf that shouldn't take any significant go changes.

[RothAndrew]

I'm planning on this being my next priority when I have more time to work on Zarf stuff. Currently still working on other projects.

[RothAndrew]

So Docker Registry uses htpasswd for password auth, which uses one-way hashes. Not as simple as just substituting ###ZARF_SECRET### with the password that Zarf creates.

Right now I'm thinking of maybe adding functionality to add parsing of ###ZARF_HTPASSWD### which would result in a proper htpasswd string like zarf-git-user:$2y$05$1oC7e2fbDJaMx7YEHIuPre90KBg2WQRRR2Ag4aE49buP7SQTu9kMS (that's the hash for the password foobar)