Req Adapter: Task max timeout fixed at 5 sec

[tuomohopia]

Req adapter timeout fixed

at 5 seconds

When using Req adapter, requests seem to be capped at 5 seconds in terms of timeouts. Because that's the default that gets passed to Task.await/2 here: https://github.com/tallarium/reverse_proxy_plug/blob/420e97abaa6c55df088be6c926653674d7442321/lib/reverse_proxy_plug/http_client/adapters/req.ex#L103.

The default comes from https://hexdocs.pm/elixir/1.17.3/Task.html#await/2.