Apache HTTP Client 5: Fix content lengths

[anuragagarwal561994]

#6747

This is referencing the above issue for Apache Http Client 5.x

In version 1.18.0 requestLength and responseLengths were removed and instead in general content-length header is being used.

The header doesn't really work in case of chunked encoding and for http client 5.x and even for content-length encoding the header is accessed before it is assigned to the request internally.

The approach followed in this MR is not really concerned about the user request content-length, but mainly the bytes transferred in and out which is more or less closely equal to the content length only. We are intercepting the byte buffers, adding the bytes in / out of the buffer.

We are storing these metrics with respect to the parent context in a virtual field. This is because there is so much disconnectivity, suggestions are welcome for an improved approach. These metrics then are collected via an attributes extractor.

[anuragagarwal561994]

@trask @mateuszrzeszutek, when you get time can you please review the changes.

[anuragagarwal561994]

Merged with #6749