Use build architecture as default platform

[Hritik14]

One possible solution to #1391

Build is taking a lot of time, Not yet tested

[Hritik14]

Can someone approve the workflows ?

[wagoodman]

Hey, I've tried this out, however, if we go this direction we still need to change some behavior. Specifically, specifying a platform override will break input sources which do not allow for specifying platform:

        2023/01/12 15:15:12 error during command execution: 1 error occurred:
                * could not fetch image "test-fixtures/cache/stereoscope-fixture-image-secrets-6dbc1b7867bf6e50c7c4f681fb9d0ac9af3fd291aae2bb643f7d268789f85c77.tar": specified platform="linux/amd64" however image source="DockerTarball" does not support selecting platform

(the CLI tests show this)

Thanks for doing all of the upfront work with anchore/stereoscope#149 , #1391 , and this PR. I can make a few mods to this and see how it work as a PoC?

[wagoodman]

On further thought, I don't think it makes sense to use the user override here to specify a default platform. I think it makes more sense to put in a fix in stereoscope conditionally based on if the user provided a platform or not (and if not, set the default based off of the host arch).

I'll open up a PR in stereoscope shortly.

[wagoodman]

See anchore/stereoscope#152