Add custom timeouts configured on gateway

We use apiman in our platform since several months.
The last version is good progress.

Sometimes we have some slow requests and we receive a timeout from apiman.
After investigating, we found still hard coded timeouts.
Changing somes in code allow us to fix the behavoir.
Do you think that is possible to make them customizable?

Here are files with hard coded timeouts:

https://github.com/apiman/apiman/blob/master/gateway/platforms/servlet/src/main/java/io/apiman/gateway/platforms/servlet/components/HttpClientRequestImpl.java#L131-L132

https://github.com/apiman/apiman/blob/master/gateway/platforms/servlet/src/main/java/io/apiman/gateway/platforms/servlet/connectors/HttpApiConnection.java#L178-L179