OpenTelemetry API should not expose Sampling related constructs

[cijothomas]

https://github.com/open-telemetry/opentelemetry-rust/blob/main/opentelemetry/src/trace/tracer.rs#L384-L408 is exposing Sampling related constructs. Sampling is a sdk (opentelemetry_sdk) concern, and these APIs should not exposed from opentelemetry crate.

Related to #2420 as these were originally exposed to special case tracing-opentelemetry

[Shunpoco]

@cijothomas Can I take this issue?

[cijothomas]

@Shunpoco Thanks for your offer to help, but this issue is not very simple despite it appearing simple!

Removing this will break tracing-opentelemetry, which is used by a lot of users! We will eventually remove it, but not yet!

#2420 is exploring how we can natively support tracing::Spans to OTel.
#2745 also discusses this.

Please look around for another issue! There are many we can use help with.

If you prefer to help with this area itself, it'd be help if we can analyze the tracing-opentelemetry crate and what APIs it uses from OpenTelemetry, and see if they can be removed. #1043 has some early discussions, but no work is actually done.

CC: @bantonsson @TommyCpp

[Shunpoco]

OK, thanks.

I will check another issue. And will also check tracing-opentelemetry if I have a spare time 😄