Send response headers

[kuniteru]

Added sending of arbitrary response headers.

Some samplers return information in the response headers that is useful for performance analysis.

For example, the BlazeMeter - Video Streaming (HLS Plugin) sampler returns the length (time) of the video segment in the response header X-MEDIA-SEGMENT-DURATION.
By comparing this value with the response time, testers can determine if testers are getting sufficient performance.

I wrote an article about sending the results of Video Streaming Sampler to Application Insights using azure-backend-listener with this change applied, and displaying the results in Application Insights Workbooks.
https://blog.pnop.co.jp/jmeter-azure-media-services_en/

If you find it effective, I would be happy to you adopt it.
The response header values are assigned to a column starting with "aih.". However, you may change it to more suitable prefix.

[adrianmo]

@kuniteru sorry for taking this long to review your PR. You did a great job by adding this new feature. I just tested it myself and it worked like a charm.

Thank you!

[kuniteru]

Thank you!