Update `slsa-provenance` predicate type

[priyawadhwa]

Once slsa-provenance v0.2 is official, we want to switch to using that in Tekton. To do this we need to:

• Update the slsa-provenance format with the v0.2 spec
• Deprecate the tekton-provenance format
• Update any pipelines using Chains for provenance generation (distroless and Tekton releases come to mind), and the

[tekton-robot]

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