Modularity configuration extension

[Net-burst]

Issue #3726 adds support to perform GET requests on the existing /openrtb2/auction endpoint in addition to POST requests. This, in turn, creates an issue with existing modularity infrastructure in the form of not being able to configure modules to run only on GET or only on POST requests.

This issue introduces a proposal for an extension to the modularity infrastructure configuration, which allows host companies to enable certain modules based on the HTTP method of the/openrtb2/auction request.

Existing configurations will continue to work as before, and modules configured to run on calls to /openrtb2/auction endpoint will be run for both GET and POST requests.

Current syntax example:

{
  "endpoints": {
    "/openrtb2/auction": {
      ...
    }
  }
}

New syntax example:

{
  "endpoints": {
    "GET /openrtb2/auction": {
      ...
    },
    "POST /openrtb2/auction": {
      ...
    }
  }
}

Module config without an HTTP method is equivalent to having identical GET and POST definitions. Only one syntax style is allowed at any given config level (host config and account config).