Add support for multiple VMRs

[premun]

Context

Right now, the service only supports one VMR which is in appsettings.json. We clone it and remember its path.
However, the service will need to target at least 3 different VMRs:

• dotnet/dotnet
• dotnet-dotnet (AzDO)
• maestro-auth-test/maestro-test-vmr

Each job will then work with the VMR it needs.

Goal

Add support for multiple different VMRs being cloned side by side and the right one being used for every job
This means making sure the metadata (VmrInfo..) points to the correct one.

We should also separate the AzDO and GitHub mirrors so that we don't push stuff by mistake.