Nginx caching metrics implementation for prometheus (#1580)

* Adding default map for nginx http metrics cache_stats

Signed-off-by: Rajesh Rajendran <rjshrjndrn@gmail.com>

* Increasing prometheus shared memory space for metrics

Signed-off-by: Rajesh Rajendran <rjshrjndrn@gmail.com>

* prometheus lua code directly from submodule

Signed-off-by: Rajesh Rajendran <rjshrjndrn@gmail.com>

* Updating default nginx config

Signed-off-by: Rajesh Rajendran <rjshrjndrn@gmail.com>

* cloning git submodules for nginx build

Signed-off-by: Rajesh Rajendran <rjshrjndrn@gmail.com>

* fix: copy all lua files from prometheus lib and config update

Signed-off-by: Rajesh Rajendran <rjshrjndrn@gmail.com>

* Updating nginx config for new prometheus metrics

Signed-off-by: Rajesh Rajendran <rjshrjndrn@gmail.com>

* Adding nginx request method to prometheus metrics

Signed-off-by: Rajesh Rajendran <rjshrjndrn@gmail.com>

* Adding nginx request method to prometheus metrics

Signed-off-by: Raje...