Move dummy OAuth to monitoring #1773

Is your feature request related to a problem? Please describe.
This repository contains the DSS product and probably shouldn't contain general dummy/test/helper tools; specifically, Dummy OAuth.

Describe the solution you'd like
Implement Dummy OAuth in the monitoring repo (probably in Python rather than Go), switch Dummy OAuth usage from the dss image to the monitoring image, then remove Dummy OAuth from this repo.

Describe alternatives you've considered
Dummy OAuth could remain in this repo and this path does not have a huge downside (hence lower priority). However, it does dilute the dss image for it to contain something other than the main DSS product, potentially slightly degrading the security stance, and potentially confusing users.

Additional context
Dummy OAuth is in this repo primarily for historical reasons rather than a current active choice.