Feature/v1.6.x support case sensitive headers

[jmclean-cnexus]

Allows for case sensitive headers, so long as config has below:
caseSensitive: true

If the above is not configured, default will be set to false, and prior functionality will persist

[jmclean-cnexus]

@hassy - please let me know your thoughts on this PR

[hassy]

Thanks for the PR @jmclean-cnexus. I agree on the need to provide a way to maintain the casing of headers for servers that don't respect the HTTP spec. The complication we have to deal with is the move from Request.js to Got.js (#802). While Request respects the casing, Got.js seems to always lowercase request headers without a way to turn that off. Since the next major release of Artillery will use Got.js we'd need to find a way to make that work.

[jmclean-cnexus]

@hassy agreed! For version 1.6.x, can we merge this. I would be happy to help out w/ the future release if needed. 1.6.x, I would imagine, would not incorporate Got.js.

[jmclean-cnexus]

@hassy just following up on this. I can do a workaround for my local use case by just overwriting the source file w/ the one in this pull request...but i know other people were asking for this capability. BTW...any reason for doing Got.js v axios? just curious...i know there are 10000 ways to skin a cat, but curious what your motive is.

[dandenton]

FYI this would help with #828 (just to link the two)

[jmclean-cnexus]

@hassy I know you're a busy guy, but any/all comments are appreciated.

[hassy]

Merged, thanks for the PR @jmclean-cnexus!

[hassy]

and published in 1.6.1 now! thanks again @jmclean-cnexus!

[BhavnaSoni1991]

@hassy , @bernardobridge Can anyone please comment if the fix for this issue is rolled back in latest releases as I am facing this issue in my test where the header name is getting changed to lower case and the tests are failing because of that?