Implement output for pipeline describe

[chmouel]

This closes #581, #640

Changes

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes tests (if functionality changed/added)
• Run the code checkers with make check
• Commit messages follow commit message best practices

See the contribution guide
for more details.

Release Notes

release-note

[tekton-robot]

The following is the coverage report on pkg/.
Say /test pull-tekton-cli-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/cmd/pipeline/describe.go	91.4%	75.9%	-15.5

[tekton-robot]

The following is the coverage report on pkg/.
Say /test pull-tekton-cli-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/cmd/pipeline/describe.go	91.4%	85.2%	-6.2

[tekton-robot]

The following is the coverage report on pkg/.
Say /test pull-tekton-cli-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/cmd/pipeline/describe.go	91.4%	85.2%	-6.2

[tekton-robot]

The following is the coverage report on pkg/.
Say /test pull-tekton-cli-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/cmd/pipeline/describe.go	91.4%	85.2%	-6.2

[vdemeester]

/lgtm

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vdemeester

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [vdemeester]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment