Improve podman build secrets docs / Makefile validatepr description

[hdub-tech]

Description

TL;DR:

1. Enhance the podman build --secret documentation and add examples.
2. Add validatepr to make help output.

Details: After struggling to find a way to build an image without writing a secret to disk first, I did some hunting. This PR is basically a copy/paste from buildah-build.1, with some tweaks to appease the podman project linter and with the addition of some Examples. (I plan to submit a similar PR to containers/buildah to update the --secret help output and add the examples there as well).

Note: This "Fixes" #23388 if you go strictly by the Title. However, if you read the comments, it looks like the OP is looking for something more along the lines of using --secret WITHOUT needing --mount=type=secret modifications to a Containerfile. This is why I omitted the issue number from the commit description. I am more than willing to modify this if requested.

Testing

• make binaries passes

• make docs passes and edits to secret.image.md appear in podman-build.1.md and podman-farm-build.1.md.

  

  

  

  

• make validatepr passes

• make help shows validatepr

  

Does this PR introduce a user-facing change?

None

[openshift-ci]

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[hdub-tech]

I confess, I did not run the full suite of tests before I put this PR up, but I'm pretty sure the 4 failures here are unrelated to my changes? Are there flaky tests here? I noticed 3 of those were timeouts.

[Luap99]

Yes these are flakes, your branch seems to based on an older commit. Please rebase to the latest main that should help in terms of machine testing on macos 6ee51c5

(In general before pushing a PR it is always a good idea to rebase to the latest main)

[hdub-tech]

Ha that's embarrassing! Usually I do make sure I've pulled latest main. I started this update weeks ago and made the mistake of trying to wrap it up late last night while tired. My apologies, I'll push a rebase later today.