Add remote sampling support instruments

[Petrovich172]

Added sdk/trace/sampling package which contains remote sampling support instruments. Such as:

• RemotelyControlledSampler — sdk/trace.Sampler implementation. Manages default sampler & perOperation samplers. Fetches sampling strategy from strategy endpoint, and updates samplers.
• ProbabilisticSampler — sdk/trace/sampling.Sampler implementation.
• RateLimitingSampler — sdk/trace/sampling.Sampler implementation.

Package is mostly based on jaeger's implementation.
Consider to close this issue

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Peter (6060c07)

[codecov]

Codecov Report

Merging #1479 (6060c07) into master (c066f15) will decrease coverage by 1.3%.
The diff coverage is 13.3%.

@@           Coverage Diff            @@
##           master   #1479     +/-   ##
========================================
- Coverage    79.0%   77.7%   -1.4%     
========================================
  Files         128     132      +4     
  Lines        6685    6820    +135     
========================================
+ Hits         5282    5300     +18     
- Misses       1148    1265    +117     
  Partials      255     255             

Impacted Files	Coverage Δ
sdk/trace/sampling/config.go	0.0% <0.0%> (ø)
sdk/trace/sampling/sampler_remote.go	0.0% <0.0%> (ø)
sdk/trace/sampling/sampler_probabilistic.go	100.0% <100.0%> (ø)
sdk/trace/sampling/sampler_rate_limiting.go	100.0% <100.0%> (ø)

[MrAlias]

Thanks for the idea and contribution. I'm going to close as this is something we would probably want to discuss the need, design, and implementation of in a Issue prior to stating this. There are many design questions here that likely need to be answered at the specification level before we can provide an implementation.

[sconover]

@MrAlias I look forward to what the otel project produces on this front - what's your expected timeframe for a design to be decided on and an impl to ship?