Change defaults: stateless temporality preference, lightstep metrics SDK

[jmacd]

Description: Changes the defaults for Lightstep's metrics SDK to use stateless temporality.

Link to tracking Issue:
Fixes #256

Testing: Also fixed a test, broken at HEAD, because I skipped a check (intentionally, but misunderstood why), see #254.

Documentation: Changelog, README.

[kayousterhout]

Can you also fix the config options table in the readme to have the correct (delta) default for the temporality? It currently says the default is false

[codecov-commenter]

Codecov Report

Merging #258 (2e436d1) into main (47a4f6e) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #258      +/-   ##
==========================================
+ Coverage   94.21%   94.32%   +0.10%     
==========================================
  Files          66       66              
  Lines        3494     3505      +11     
==========================================
+ Hits         3292     3306      +14     
+ Misses        155      152       -3     
  Partials       47       47              

Impacted Files	Coverage Δ
launcher/config.go	88.94% <ø> (ø)
...dk/metric/aggregator/histogram/structure/config.go	100.00% <ø> (ø)
.../sdk/metric/aggregator/histogram/structure/test.go	100.00% <ø> (ø)
pipelines/metrics.go	67.93% <ø> (+2.29%)	⬆️
...tric/aggregator/histogram/structure/exponential.go	96.67% <100.00%> (+0.12%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.