Ability to use specific platform when generating ImagesLock

[gabegorelick]

Describe the problem/challenge you have

kbld is often used to generate lockfiles that are passed to imgpkg to generate a bundle. When such a lockfile contains a multi-platform image index, the resulting imgpkg bundle will include all images in the index. This is great if you need to distribute the bundle to a lot of different platforms, but if you know the exact platform you're targeting then including all those other platform images in the bundle wastes a lot of space (Windows images in particular can be very large).

Describe the solution you'd like
kbld should be able to replace index references with specific images based on the desired platform (OS, architecture). That way, imgpkg won't bundle up unwanted images.

Anything else you would like to add:
Discussed in https://kubernetes.slack.com/archives/CH8KCCKA5/p1639157591175300

---

Questions:

1. what should the UX be?
   • command-line args (e.g. --force-arch=X --force-platform=Y)
   • addition(s) to kind: Config
2. should origins: include the platform/architecture supplied by the user? (more generally, should we include the total command-line used?)
3. ...

---

Vote on this request

This is an invitation to the community to vote on issues, to help us prioritize our backlog. Use the "smiley face" up to the right of this comment to vote.

👍 "I would like to see this addressed as soon as possible"
👎 "There are other more important things to focus on right now"

We are also happy to receive and review Pull Requests if you want to help working on this issue.

[pivotaljohn]

For use cases where both producing and deploying the artifacts are under the control of the same party, this seems particularly useful.

There are a number questions to flesh out before we begin (see description and Slack convo).

[cppforlife]

in progress: #234