feat: Publish SBOM for Keptn artifacts/images

[riteshsonawane1372]

This PR

Added Sboms for Keptn services and CLI using the anchore SBOM action

Related Issues

Fixes #7163

[mowies]

This is a good start! But there's some stuff missing still.
First of all, you could use the matrix we already have in place in the docker_build job.
Something like this:

build_sboms:
  name: Build SBOMs
  needs: [release-please, prepare]
  strategy:
    matrix: ${{ fromJson(needs.prepare.outputs.BUILD_MATRIX) }}
  steps:
  - name: SBOM ${{ matrix.config.artifact }}
    uses:  anchore/sbom-action@v0.13.1
    with:
      format: spdx
      path: ./${{ matrix.config.working-dir }}
      artifact-name: sboms

This uses the matrix with all artifacts and then it should pack them all into the same artifact.
After this, we need a another step to attach that sboms artifact to the release though.
You can essentially do something like this

[sonarcloud]

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