Ability to look up the PVC name

[jlpettersson]

Expected Behavior

That I can "look up" the PVC name for a workspace using variable substitution.

Use case
In larger organizations using Microservice architecture and Kubernetes, it is common to organize for autonomous application teams and platform teams. For compliance, application teams may not have direct access to production environments, but only through a CI/CD system. When using this team organization, it is benificial if app-teams can define the CI/CD pipeline in their application git repository, similar to e.g. a Jenkinsfile or cloudbuild.yaml. When adopting Tekton, we have created our own pipeline.yaml DSL file. Our setup is as follows (also e.g. Jenkins X is architected for such usage).

Trigger -> Pipeline{ Task(git-clone to workspace) -> Task(parse pipeline.yaml and generate Pipeline and initiate PipelineRun for the generated Pipeline } 

In the Pipeline above, the first task clones the repository to a workspace volume and then a new pipeline+run is generated, it would be useful if we can reuse the workspace instead of doing a second identical git clone again.

It would be very useful if I could use variable substitution to "look up" the PVC name for the workspace in this use case, e.g. with $(workspaces.ws-name.claim). Similar to how I can use $(workspaces.ws-name.volume) to get the volume name in a TaskRun.

Actual Behavior

When using PersistentVolumeClaim as a volume source for a workspace, the PVC name is already known. But when using VolumeClaimTemplate as a volume source, there is no way to "look up" the PVC name.

/kind feature
/assign