Introduce a timeout notion JUST for the pending acquire case

[simonbasle]

Calling Pool#acquire().timeout() (the vanilla timeout operator) introduces a timeout that can effectively trigger in two cases:

• the pool is depleted and cannot allocate more resources: timeout on pending acquire (time waiting for a resource to be released)
• the pool is depleted BUT can allocate new resources: timeout on the allocation of one new resource

It appear that in some cases, the resource allocation can take some more or less arbitrary time that we are ok waiting for if we now we'll end up with a resource, but we don't want to wait more than necessary if we know we can't allocate more resources.

i.e. we want a timeout on the pending case only.

[simonbasle]

to be ascertained:

• A. should the timeout be configured in the acquire call (ie overload acquire(Duration)) or in the pool configuration?

[violetagg]

@simonbasle Currently in Reactor Netty we have this setting only on the connection pool, you are not able to change this for a particular acquire operation.

[simonbasle]

as discussed off-band, we'll keep the acquire(Duration) overload only. global configurations can be put in place easily enough in downstream libraries.