Agentless running jobs asynchonously

Hi,

I am really excited to see agentless steps coming to Teamcity. One point I'm missing is the ability to use the agent itself for running the task you are waiting on.

For example in the case of building OSx application, signing and notarizing the application can take a long time (say 10 minutes), and does not uses much of the agent resources. I would love to be able to say "what's coming up is going to take a long time, but the agent is free to do something else".

I've noticed the note from the documentation that says `We highly recommend releasing the agent only during the last build step. Make sure the tasks performed outside TeamCity do not require the build agent.` which makes this feature unusable in the above use case.