Add custom sampler project

[reyang]

This is very similar to #996.
Trying to use the docs and tutorial projects to drive for better design and implementation.
This change should give us some idea about the sampler use case.

Changes

• Added custom sampler tutorial project

[codecov]

Codecov Report

Merging #1001 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1001   +/-   ##
=======================================
  Coverage   68.42%   68.42%           
=======================================
  Files         220      220           
  Lines        5989     5989           
  Branches      981      981           
=======================================
  Hits         4098     4098           
+ Misses       1619     1617    -2     
- Partials      272      274    +2     

Impacted Files	Coverage Δ
...nTelemetry/Internal/OpenTelemetrySdkEventSource.cs	80.88% <0.00%> (-5.89%)	⬇️
src/OpenTelemetry/Metrics/CounterMetricSdkBase.cs	93.33% <0.00%> (+13.33%)	⬆️

[CodeBlanch]

LGTM! Issue with the sampler is we only currently allow true/false response but by the spec there should be 3 states?

[reyang]

LGTM! Issue with the sampler is we only currently allow true/false response but by the spec there should be 3 states?

That's already showing the value of having these simple tutorials - if we're unhappy with the tutorial projects, we know we got to fix something 😄.

[cijothomas]

LGTM! Issue with the sampler is we only currently allow true/false response but by the spec there should be 3 states?

It's tracked as an issue tagged p1 for coming release. @rajkumar-rangaraj will be working on it