Implement vhost_traffic_status_upstream_no_cache filter

[heikkiorsila]

This enables monitoring upstream backend events that are configured not to use cache.

Add the following line to nginx config to create a group:

    vhost_traffic_status_filter_upstream_no_cache "NO_CACHE";

[vozlt]

Thanks for the pull request for improvement. But do you need to put non-cached statistics inside serverZones? As far as I know you can already use the information(miss, bypass, expired, stale, updating, revalidated, hit, scarce) in serverZones to calculate statistics for non-cached items. I think it is correct to calculate it through a 3rd party program.

[u5surf]

@ypcs Hi, Thanks following about this PR.

We almost agree with what @vozlt said the below

But do you need to put non-cached statistics inside serverZones? As far as I know you can already use the information(miss, bypass, expired, stale, updating, revalidated, hit, scarce) in serverZones to calculate statistics for non-cached items. I think it is correct to calculate it through a 3rd party program.

Do you have any another reasons that the feature is necessary for this modules? And can you add some tests or share your expected scenarios to explain the necessity on this feature? We'll judge based on it whether this PR should merge or not.

[ypcs]

Hi. We're currently evaluating if this is necessary, I'll post update later, and we'll provide tests then.