feat(pipelineloop): Support workspaces for pipelineLoop.

[ScrapCodes]

Which issue is resolved by this Pull Request:
Resolves #786

Description of your changes:
Added support for supporting workspaces in pipelineLoopSpec.
Added tests and examples.

Environment tested:

• Python Version (use python --version):
• Tekton Version (use tkn version):
• Kubernetes Version (use kubectl version):
• OS (e.g. from /etc/os-release):

Checklist:

• The title for your pull request (PR) should follow our title convention. Learn more about the pull request title convention used in this repository.

[Tomcli]

thanks @ScrapCodes for the quick PR
/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ScrapCodes, Tomcli

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