The TDS documentation specifies that the TDS_OWNER and TDS_KEY should be added to the environment variables of the build server. Does this mean the Windows environment variables through control panel, build configuration variables, or something else?
The TDS_Owner and TDS_KEY variables are only required when using cloud builds. This is because you obviously can't install TDS through the MSI on 'the cloud'.
For regular build servers, you just need to install TDS using the MSI, and enter your license details in the steps in that wizard.
For cloud builds, you should have the ability to add environment variables to the build settings. For instance, when I use AppVeyor, I can select Project->Settings->Environment, and add these variable there. For VSTS (which is cloud TFS), you should be able to just add a build variable for each of these settings.