WHAT

Refine the content for the Producing and consuming messages quick start:

https://github.com/redhat-developer/app-services-guides/pull/552

DONE

• Content is refined to meet CCS and RH standards so that it's appropriate for both upstream and downstream

• • Downstream: On the Portal (location TBD)
• Content has been tested for accessibility 
  • https://docs.google.com/document/d/1SXhLknoE4gjyqumlCEI6H_IOekcjjPyjiNjccysyzcM/edit#heading=h.cnle8410kh73
  • This may require some collaboration with UXD for any content that appears in the UI.
• Content is ready for QE testing