Allow configuring Netty compression content size threshold

[wvuong]

Motivation:

Netty allows you to customize the minimum content size threshold for compression via a constructor arg in HttpContentCompressor. Configuring this means that Netty won't compress responses if they are below the size threshold which can be useful for small responses where the CPU vs saved bytes tradeoff is not good. The Netty default is 0 which I carried on here. I also updated the documentation.

Conformance:

I have signed the Eclipse Contributor Agreement.

[vietj]

@wvuong we need a test for this that checks that the threshold is taken in account

[wvuong]

Sure, I'll put something together in the next day or two.

[vietj]

thank you