Modsecurity: Implement the support to setenv action

[zimmerle]

setenv action is not implemented on ModSecurity version 3.0 yet.

[dune73]

Adding this would be very helpful for me. It's very important in my methodology, even if I am not sure how to display the vars in nginx.

[cyberblackhole]

any update on setenv? my current version is v3.0.2. I get the below error on configtest

Action: SetEnv is not yet supported.

[zimmerle]

Implemented at: bc3d3f19154793e23568103b931a15168b34d768