Redundant naming in `poolConfiguration`

[weissi]

async-http-client/Sources/AsyncHTTPClient/HTTPClient.swift

Line 645 in 2e6a64a

public var poolConfiguration: PoolConfiguration

The new poolConfiguration property sits inside a configuration object so often, users will type

HTTPClient(eventLoopGroupProvider: ...,
    configuration: Configuration(poolConfiguration: ...)

the word "configuration" appears way too much here. We can't fix all instances anymore but the worst example is probably poolConfiguration which isn't released yet so we should fix it. The other sibling properties also don't have the word "configuration". We could for example name it connectionPoolParameters or maybe just connectionPool?

I also think we shouldn't use the word "pool" without "connection" in a public API, users will probably wonder what is being pooled as we may be pooling other things (not just connections).

[I marked it release blocker for now because this can only be done before 1.2.0, feel free to remove if you think this is too much]