Remove creds logs

[grallewellyn]

Purpose

Credentials for dockerhub and dockstore are no longer printed in the logs upon an error or printed in the details section when running the DAG
This is because we switched to using kubernetes secrets to manage these credentials

Proposed Changes

• [CHANGE] Dockerhub and dockstore credentials now handled with kubernetes secrets

Issues

unity-sds/unity-project-management#228
#398

Testing

• tested that passing an invalid github url doesn't result in errors with credentials being printed to the logs
• tested that passing a valid github url that is to a blank repo doesn't result in errors with credentials being printed to the logs
• tested that this successfully uploads to dockerhub and dockstore with the right credentials
• I can run this DAG successfully in my SPS deployment with the git url as https://github.com/unity-sds/unity-example-application

[LucaCinquini]

I tested deployment and execution, it works great.
I am also glad that we now have a working example on using the Kubernetes secrets within SPS and a DAG.