A container workflow similar to the generic workflow that allows users to build a container themselves in the user workflow and then generate provenance for it.

• Add container generator workflow (Add a generic container workflow #471)
• Pre-submit test ([feature] pre-submit test for container workflow #604)
• e2e tests ([feature] e2e tests for container generator workflow #603)
• Documentation
  • Basic usage (Add a generic container workflow #471)
  • [docs] Verifying provenance with Kyverno #389
  • [docs] Verification with sigstore-policy-controller #491