Merge observability report sender for all signals, remove duplicate code

[bogdandrutu]

Depends on #12164

[codecov]

Codecov Report

Attention: Patch coverage is 92.77108% with 6 lines in your changes missing coverage. Please review.

Project coverage is 91.75%. Comparing base (689d43e) to head (92defee).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
exporter/exporterhelper/internal/obs_report.go	90.90%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12165      +/-   ##
==========================================
- Coverage   91.76%   91.75%   -0.01%     
==========================================
  Files         463      464       +1     
  Lines       24809    24766      -43     
==========================================
- Hits        22766    22725      -41     
+ Misses       1659     1656       -3     
- Partials      384      385       +1     

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[jade-guiton-dd]

The only behavior change here is renaming span attributes from (taking spans as example) sent_spans / send_failed_span to a generic items.sent / items.failed, right? (Just confirming, since I'm in the process (#11140) of reviewing the telemetry we have on the OTLP exporters)

[jmacd]

The only behavior change here is renaming span attributes from (taking spans as example) sent_spans / send_failed_span to a generic items.sent / items.failed, right?

Is that intentional? We can't skip the changelog for a change like that.

[bogdandrutu]

@jmacd added changelog