Set up test environment for backflow dogfooding

[premun]

Context

Similarly to Maestro, we will need a staging environment for VMR codeflow purposes over which we will run the E2E tests.
We will need a test VMR and some test repositories which we will flow code between.

It might be better that we start off with real repositories and a test VMR so that we can see what kind of content is synchronized into the VMR so that we can create an E2E PoC. If we are flowing changes from well-known repositories (like the ones we own), we could easily validate the content.

Eventually, we can create test repositories too and prepare some more advanced E2E tests that verify more complex flows.

Goal

• Create a test VMR called dnceng-vmr in the maestro-auth-test organization
• Set up the VMR to contain 3 of our repositories - dotnet/dnceng, dotnet/dnceng-shared, dotnet/arcade-services

Once we have this, and we have tested the code flow, we will need to flow the other way as well (e.g. make a change in src/arcade-services and flow it to the real repo). For that, we will need the VMR to produce a real BAR build but that's a stage 2 and not part of this issue.

The follow-up to this will be a full E2E tests with BAR builds between a test VMR and test repositories.

[premun]

I created https://github.com/maestro-auth-test/dnceng-vmr

[premun]

I think this is done for the moment. We will revisit.