feat: add additional handling of prometheus-cache in ngx_tpl.lua

[qihaiyan]

Description

{% if enabled_plugins["prometheus"] and not enabled_stream_plugins["prometheus"] then %}
    lua_shared_dict prometheus-metrics {* http.lua_shared_dict["prometheus-metrics"] *};
    -- add prometheus-cache here
    lua_shared_dict prometheus-cache {* http.lua_shared_dict["prometheus-cache"] *};
{% end  #%}

Maybe it's better to set prometheus-cache together with prometheus-metrics in ngx_tpl.lua

[Baoyuantop]

Do you think there are any problems with the current approach?

[qihaiyan]

Do you think there are any problems with the current approach?

Only when use_apisix_base is set to true, will the prometheus-cache take effect.
But in order to integrate with QAT, i used a custom built openresty instead of apisix-runtime, so use_apisix_base is not true, and prometheus-cache is not setted in nginx.conf even if prometheus plugin is enabled. @Baoyuantop

[Baoyuantop]

Got it, welcome to submit PR to optimize this part.

[Baoyuantop]

Hi @SkyeYoung, could you help confirm this issue?