Add the ability to specify a timeout on a function level

Currently functions can run forever on dedicated app plans. I'm fine with this, but on some of my processing functions need fine grained timeouts. If it doesn't finish in 20 seconds it will never finish and I want to kill it. There currently doesn't seem to be a way to do this today.

Start by reading the Azure Functions host/runtime handling for dedicated-plan execution and any existing timeout configuration. Confirm how a function-level 20-second limit should interact with the current plan behavior, then verify that an invocation exceeding the configured limit is terminated and that the existing behavior remains unchanged when no function-level timeout is set.

Written by the indexing model from the issue text.