Add option to enable trace sampling

[grcevski]

This PR adds a configuration option to enable trace generation sampling. Sampling with ParentBased and TraceIDRatio are recommended as per the OTEL spec https://opentelemetry.io/docs/instrumentation/go/sampling/.

By default our sampling remains at 1.0, which means everything is sent, however it can be configured as little as 0.

[codecov-commenter]

Codecov Report

Merging #238 (372fa91) into main (c73c3a7) will decrease coverage by 4.62%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #238      +/-   ##
==========================================
- Coverage   80.78%   76.16%   -4.62%     
==========================================
  Files          37       35       -2     
  Lines        3065     3008      -57     
==========================================
- Hits         2476     2291     -185     
- Misses        438      539     +101     
- Partials      151      178      +27     

Flag	Coverage Δ
integration-test	76.16% <100.00%> (+<0.01%)	⬆️
unittests	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
pkg/internal/pipe/config.go	28.20% <ø> (-28.21%)	⬇️
pkg/internal/export/otel/traces.go	72.54% <100.00%> (-16.45%)	⬇️

... and 8 files with indirect coverage changes

[MattFrick]

Looks good. Should there be a test that does a sampling ratio other than fully on or off?

[grcevski]

Looks good. Should there be a test that does a sampling ratio other than fully on or off?

I was thinking about it, but I'm struggling to make one that won't be flaky. Maybe at 50% I can double the events and check if I get half. I'll try that.