Support mode to generate queueUrl from incoming request, rather than static hostname.

[nhoughto]

The current behaviour as I understand it is to configure a static hostname (or allow it to default to localhost) and then that value is used to create the queueUrl that clients will follow to do SQS ReceiveMessage etc.

This works in simple situations but breaks scenarios where a single goaws instance might have multiple ingress paths, think Kubernetes Service vs Kubernetes Ingress vs Kubernetes NodePort.. there are lots of reasons this can happen.

To solve this problem it would be great if you could configure a mode where the hostname used in the queueUrl is derived from the incoming request rather than from configuration or defaulted. This limits the number of "environments" you can have, I expect you can only have 1 in "derive" mode, but i'd expect most users have just one environment anyway.

[nhoughto]

Seems to be mostly solved by #213
That appears to be changing the default behavour from localhost to using the host header tho, which is possibly undesirable.

I made an alternative version of the fix too here:

bsycorp@2f32176

[p4tin]

PR?

[nhoughto]

way late 😬
#234