use docker to generate and attest SBOMs

Right now Keptn is using anchore/sbom-action to generate SBOMs for images which generates SBOMs post the build process. This PR adds docker/build-push-action to generate and attest the SBOM during the release pipeline.

Fixes #3309

How to test

• Manual Test A
• Unit Test B
• Integration Test C

Checklist

• My PR fulfills the Definition of Done of the corresponding issue and not more (or parts if the issue is separated
  into multiple PRs)
• I used descriptive commit messages to help reviewers understand my thought process
• I signed off all my commits according to the Developer Certificate of Origin (DCO)
  see Contribution Guide
• My PR title is formatted according to the semantic PR conventions described in
  the Contribution Guide
• My code follows the style guidelines of this project (golangci-lint passes, YAMLLint passes)
• I have performed a self-review of my code
• My changes result in all-green PR checks (first-time contributors need to ask a maintainer to approve their test runs)
• New and existing unit and integration tests pass locally with my changes