Return compose request details as part of metadata response

[bcl]

This pull request includes:

• adequate testing for the new functionality or fixed issue
• adequate documentation informing people about the change such as
  • submit a PR for the READMEs listed here
  • submit a PR for the osbuild.org website repository if this PR changed any behavior not covered by the automatically updated READMEs

[schuellerf]

If I got it correct, this is only for on-prem as it will be empty in the service, right?
To get it consistent we would need to extend image-builder to also return the request by just getting it from the image-builder DB (json or postgres) in a subsequent PR.
otherwise it LGTM

[schuellerf]

Two questions aside:

• where does the issue (triggering this PR) come from, which problem does it solve?
• is this ComposeMetadata → request (similar to the ComposeMetadata → packages) big? would it make sense to be able to mask it in the getComposeMetadata request by something like getComposeMetadata → hide_{packages,request}

(it's a bit confusing that there is a request in the response, but I hope my comment is somehow readable)

[bcl]

This is part of https://issues.redhat.com/browse/COMPOSER-2131 (which is also related to cockpit-composer using cloudapi instead of weldr).

The request is in the response because I want to reuse the openapi structure instead of reinventing and copying, etc. I don't think size is a consideration, it will be as big as the original request so I don't see any reason to complicate things by trying to hide it.

ETA: And yes, it is on-prem only for now, conditional on the artifact directory being used. Using the db is beyond the scope of this PR and can be added later if needed.