Add Tekton Chains and Sigstore to the demo

[rcarrata]

https://github.com/tektoncd/chains

https://gkovan.medium.com/a-zero-trust-approach-for-securing-the-supply-chain-of-microservices-packaged-as-container-images-89d2f5b7293b

https://github.com/ztsc/tekton

[MoOyeg]

Started this feature - https://github.com/MoOyeg/devsecops-demo.git. I will push when complete.