Print JSON objects to stdout without a wrapping array

[luxas]

Hi! This builds on top of #2195; please review only the second commit.

This is just an improvement suggestion of slightly personal taste. I think it's a bit nicer JSON to look at, if the objects are marshalled as { ... } { ... } { ... } instead of [ { ... } ][ { ... } { ... } ] (depending on how the exporter is used). Printing only JSON objects is consistent with JSON loggers like zap, for instance.

What do you think about this? I have seen and understood #1819; this is more of a cosmetic change.

[codecov]

Codecov Report

Merging #2196 (1585d76) into main (add511c) will decrease coverage by 0.0%.
The diff coverage is 75.0%.

@@           Coverage Diff           @@
##            main   #2196     +/-   ##
=======================================
- Coverage   72.9%   72.9%   -0.1%     
=======================================
  Files        177     176      -1     
  Lines      12161   12161             
=======================================
- Hits        8869    8867      -2     
- Misses      3054    3055      +1     
- Partials     238     239      +1     

Impacted Files	Coverage Δ
exporters/stdout/stdouttrace/trace.go	75.5% <75.0%> (-0.1%)	⬇️
...s/otlp/otlptrace/internal/connection/connection.go	14.8% <0.0%> (-1.6%)	⬇️

[MrAlias]

This needs a changelog entry describing the change, especially since it is going to change the data format users will be working with.

[luxas]

Thanks for the merge of #2195 and reviews 💯!
I rebased this now and added a changelog entry.

[lizthegrey]

This introduces a race condition because the JSON encoder object is now shared between invocations, and can be potentially called in parallel (trampling its own buffer); I'm opening a PR to fix.