Documentation on why waagent manages routes

On other public cloud networks (e.g. AWS), the dhcp server provides the network address to the VM as well as routes. However this does not seem to be the case on Azure, and the `waagent` seems to be responsible for adding the default route.

Some questions:
1. where can I find azure documentation on how this works (and why it works this way, differently from other public clouds like AWS).
2. how can i configure waagent to perform only this function (set up routes) and manage **nothing** else? Will setting all config elements to `n` suffice?
3. The docs are not clear as to which config knobs controls the addition of the default routes. Is it the `Provisioning.Enabled` setting?

Start with the Azure networking and waagent documentation referenced by the questions, then trace the documented configuration around Provisioning.Enabled. Done means the docs explain why routes are handled this way, identify the route-setting control, and state whether disabling all other settings leaves route management alone.

Written by the indexing model from the issue text.