Recommend use of initializers for config structs

[Aneurysm9]

Updates style guide and changes existing configure() implementations to newConfig() as appropriate.

[codecov]

Codecov Report

Merging #1163 into master will increase coverage by 0.0%.
The diff coverage is 80.0%.

@@          Coverage Diff           @@
##           master   #1163   +/-   ##
======================================
  Coverage    77.9%   77.9%           
======================================
  Files         135     135           
  Lines        7191    7192    +1     
======================================
+ Hits         5602    5604    +2     
+ Misses       1346    1344    -2     
- Partials      243     244    +1     

Impacted Files	Coverage Δ
exporters/otlp/options.go	51.7% <55.5%> (ø)
api/trace/tracetest/config.go	91.8% <100.0%> (ø)
api/trace/tracetest/provider.go	100.0% <100.0%> (ø)
exporters/otlp/otlp.go	79.3% <100.0%> (+0.1%)	⬆️
exporters/stdout/config.go	72.0% <100.0%> (ø)
exporters/stdout/exporter.go	26.6% <100.0%> (ø)
sdk/trace/batch_span_processor.go	79.5% <0.0%> (+1.0%)	⬆️

[XSAM]

LGTM 🚀