Implement Host header bypassing

[ffix]

This pull request adds the ability to bypass the Host header in Reproxy for compatibility with services like Grafana as mentioned in #133.

It includes the following changes:

• A global option has been added to enable bypassing the Host header for the entire Reproxy instance.
• A per-container trigger has been added to enable or disable bypassing the Host header on a per-container basis.

It hasn't been tested with a consul catalog as me don't' have access to one.

I'm not familiar with the coding standards of this project, so I would appreciate any comments or fixes. 

[Semior001]

Is there any chance of being added? Still waiting for being able to use grafana :)

[umputun]

@ffix - I have updated your branch with all the current changes from the master. It had a lot of conflicts, but hopefully, I have them adequately resolved. Pls, take a look and let me know if everything is fine

[MrZoidberg]

@ffix @umputun any progress with this? tried to run Grafana behind reproxy and failed with same problem. Any help needed?