Add acceptance tests

[lcarva]

Similarly to the acceptance tests in enterprise-contract/ec-cli, let's add some tests here that execute against the output of services/apps, instead of mocked data.

Acceptance Criteria

• Create at least one test that executes against the provenace attestation output provided by Tekton Chains.
• As part of the test execution,
  • Spin up a new Kubernetes-like cluster, e.g. kind
  • Install Tekton Pipelines and Tekton Chains.
  • Spin up an OCI registry.
  • Execute a Pipeline that generates an image which is then signed and attested by Chains.
• An EC contributor should be able to execute acceptance tests on their laptop without requiring access to a managed service, e.g. AWS account to create a cluster.

Do consider copying the "framework" from ec-cli.

There's quite a bit of work in implementing these acceptance tests, so let's keep the first test very very simple. Things that are out of scope:

• Identity based signatures (aka keyless)
• Any sort of Rekor integration
• Anything that is not strictly necessary to achieve the acceptance criteria