Feature Request: Ability to control request timeout > 120 seconds

Currently, if any request takes longer than 120 seconds, the following exception gets raised:
> TimeoutError: Request timed out after 120 seconds.

This appears to be controlled by the `invocation.INVOCATION_TIMEOUT` constant and does not appear tunable. I see that the constructor for `Invocation` takes in a `timeout` parameter that defaults to that constant value, but as far as I can tell there's no way to get a timeout actually passed-in to the `Invocation` object since that's all handled under-the-hood when the client is configured.

I would love it if I could control the timeout on a per-request basis.

Start with the invocation.INVOCATION_TIMEOUT constant and the Invocation constructor's timeout parameter, then trace how client configuration creates Invocation objects. Identify the request entry point where a per-request timeout could be supplied. Done means callers can control the timeout for an individual request rather than being limited to 120 seconds.

Written by the indexing model from the issue text.