Improve ergonomics of "zarf init" for those building from source

[bradclawsie]

Is your feature request related to a problem? Please describe.

Building zarf from source, I was unable to naively run zarf init.

Describe the behavior you'd like

• Given a user building zarf from source, obtaining a binary instrumented with the commit hash
• When that user attempts to run zarf init
• Then the corresponding init pkg will not be found, as the commit hash of the built zarf binary will be part of the oci reference.

Describe alternatives you've considered

Assuming it is acceptable for a user building from source to expect zarf init to work, some alternatives to just failing the package pull:

1. Just use the init pkg from the last major version
2. Provide users with some simple messaging of how to create their own init pkg locally

[brandtkeller]

I think this can be improved but I want to ensure we don't create more confusion for standard CLI users in favor of a better developer UX.

I personally prefer that a binary built from source not default to the latest-released init package as that could impact local development expectations.

We may need to think on this more before implementation to ensure this doesn't confuse or regress intended persona logic.