cloudapi: Add /distributions/ to cloudapi

[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

[bcl]

I'm thinking I want to extend this to return more, so converting to draft for now.

[github-actions]

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[thozza]

Thanks for the change.

I don't understand the reason behind returning the full repository configuration for each distro/arch/image_type combination from this endpoint. I think that I'm missing the bigger picture behind this change, especially since the linked Jira task talks only about listing the matrix of supported distro:arch:image_type and nothing about repositories.

In addition to that, The summary of the PR is in contradiction to what this PR does - adding only /distributions/ endpoint and not /distributions/{arch}.

Lastly, I'm not sure if it is a good practice for API to use values as object property names in the returned JSON. IOW, the implemented approach vs. to return a flattened array of objects such as:

[
    {
        "distro": "test-distro-1",
        "arch": "test_arch",
        "image_types": [
            "test_type"
        ]
    },
    ...
]

[bcl]

I'm trying to remember why I included the actual repo data, and I think it was because we've had some questions about exactly what repos are being used for a build and no way to query that info. It's useful info, and easily available, so I included it.

As for the openapi layout, I couldn't figure out any other way to do it and have variable named keys. The reason for that is that it makes more sense to process the output using keys than it is to have to search through all the results for the distro+arch.

The output from this will be used with composer-cli in order to let the user explore what's available to use for the builds, so more detail is better.