Adding yml to accepted output formats

[warango4]

Pull request

What this PR does / why we need it

Add support for yml extension when user wants to output a resource through workload get or workload list commands.

Output will be same if user wants to show it with yaml format.

Usage example:
tanzu apps workload get my-workload -oyml
tanzu apps workload list -oyml

Which issue(s) this PR fixes

Fixes #72

Describe testing done for PR

• Unit testing in source code
• Used commands in local cluster

Additional information or special notes for your reviewer

Signed-off by: Wendy Arango warango@vmware.com

[odinnordico]

LGTM

[heyjcollins]

Acceptance

tanzu apps workload get

• workload get my-app -o yml && workload get my-app -o yaml
  • confirmed yaml returned with no additional content
  • validated yaml is syntactically correct
• workload get my-app -o json
  • confirmed json returned with no additional content
  • validated json is syntactically correct
• workload get misnamed-app -o yml && workload get misnamed-app -o yaml && workload get misnamed-app -o json
  • confirmed correct error message returned (not as yaml/json)

    Workload "default/misnamed-app" not found
    Error: exit status 1
    
    ✖  exit status 1
    

---

tanzu apps workload list

• workload list -o yml && workload list -o yaml
  • confirmed yaml returned with no additional content
  • validated yaml is syntactically correct
• workload list -o json
  • confirmed json returned with no additional content
  • validated json is syntactically correct
• workload list -o yml -n wrong-namespace && workload get misnamed-app -o yaml && workload get misnamed-app -o json
  • validated yaml returned is empty and syntactically valid

    ---
    []
    

  • validated json returned is empty and syntactically valid

    []