Add the OpenTelemetry Sampler and the sampling rate configuration

Just adding some thoughts here, this might be a separate issue.

🌱 Ideas and feedback Active gave me feedback and referenced this about the sampler rate. This is useful, but what I was thinking about there was a bit different.

I'm still reading into OpenTelemetry, I have experience with Blackfire and New Relic. Both have this concept of collecting minimal information about most/all requests and then provide detailed traces for some requests. New Relic does that for slow requests, Blackfire randomly picks some requests to trace in more depth or you can request it manually.

I think the amount of data those provide is probably way too heavy for OpenTelemetry and the span structure, but it could be be very useful to have a two-layer plugin system. Some plugins like Exceptions should always run, but for example I'd only want see database queries for every 1/1000th request or something. Could be controlled by an event, so more complex conditions can be implemented.