EdgeX DevOps: Fully Automate DockerHub description/overview updates

[ernestojeda]

Fully automate Dockerhub description pipeline. Currently, it is broken into two steps and can be error-prone.

https://github.com/edgexfoundry/cd-management/tree/edgex-docker-hub-documentation

The pipeline changes:

• Pipeline should always call generate-overviews.py --offline.
• If there any changes to the generated overviews, then those changes should be committed to the repo and then pushed with a special commit message.
• After the merge of the pipeline, a user could run the job manually to apply the changes to DockerHub.