Split http and stream variants

[jirutka]

It builds ngx_http_dynamic_upstream_module with ngx_module_type=HTTP, but it actually provides support even for the stream context and hence links the stream module. That’s quite unexpected.

Can you please split the module into http and stream variants? You can take inspiration from https://github.com/kjdev/nginx-keyval or https://github.com/leev/ngx_http_geoip2_module.