feat(tracing): route/service scoping

[StarlightIbuki]

implement KAG-244

[fffonion]

I feel like we are mixing the source of truth of "whether to trace or not" in different places. Previously when
otel plugin can only be global:

1. we have a opentelemetry_tracing config that tells Kong whether to collect specific instrumentations
2. we have otel plugin that controls whether and where a collected spans needs to be flushed to

In this PR we have an additional source of truth on "whether to trace or not" depending on if any of a tracing
plugin (otel in this case) is enabled on current path, and that conflicts with fact that it's previously only
controlled by opentelemetry_tracing. So i would suggest we refactor the implementation a bit so that:

1. we still rely on opentelemetry_tracing config that tells Kong whether to collect specific instrumentations
2. rely on plugins_iterator to pick a plugin on current request, if such otel plugin exists, then its log phase
   phase handler is executed, and spans are flushed.

so that we don't need complex logic over iterration over plugins and cache invalidations.

[StarlightIbuki]

I feel like we are mixing the source of truth of "whether to trace or not" in different places. Previously when otel plugin can only be global:

1. we have a opentelemetry_tracing config that tells Kong whether to collect specific instrumentations
2. we have otel plugin that controls whether and where a collected spans needs to be flushed to

In this PR we have an additional source of truth on "whether to trace or not" depending on if any of a tracing plugin (otel in this case) is enabled on current path, and that conflicts with fact that it's previously only controlled by opentelemetry_tracing. So i would suggest we refactor the implementation a bit so that:

1. we still rely on opentelemetry_tracing config that tells Kong whether to collect specific instrumentations
2. rely on plugins_iterator to pick a plugin on current request, if such otel plugin exists, then its log phase
   phase handler is executed, and spans are flushed.

so that we don't need complex logic over iterration over plugins and cache invalidations.

🤦‍You are right. The code could be much more straightforward. I am rewriting the code.