Promote SLSAv1.0 offering of Chains format to `beta`

[chitrangpatel]

This was discussed at the Chains WG on July 18th. Since SLSAv1.0 was released, Chains provided support for it starting with provenance format slsa/v2alpha2. At this point, it is slsa/v2alpha4 (which includes support for StepActions and StepResults).

We propose stabilizing this to a Beta version: v2beta1 so that there is reduced immediate breaking changes and our users can adopt it more.

Here, I highlight some missing items:

• Implement support for Tekton Artifacts. The final PR is under review and we can introduce support for it in Chains right after.
• Identify the name of the pipelineTask/pipelineRun/taskRun/Step using the remote resource (Pipeline, Task, StepAction) in the resolved dependencies and byProducts. This will help with completeness.
• Capture the origin of a remote StepAction (i.e. uri and digest) in the resolved dependencies: https://github.com/tektoncd/pipeline/pull/8106

[chitrangpatel]

cc @lcarva @renzodavid9

[chitrangpatel]

@renzodavid9 please add any other items here that I may have missed.

[renzodavid9]

With https://github.com/tektoncd/pipeline/pull/8106 merged we can implement last point from https://github.com/tektoncd/chains/issues/1160#issue-2417114302, I'll take a look an open a PR for it

[PuneetPunamiya]

@chitrangpatel @renzodavid9 I'll work on this part

• Identify the name of the pipelineTask/pipelineRun/taskRun/Step using the remote resource (Pipeline, Task, StepAction) in the resolved dependencies and byProducts. This will help with completeness.