leverage tracer provider to set service name for Zipkin exporter

[gruebel]

Fixes #
Design discussion issue (if applicable) #

Changes

• continuation of feat: Replace Zipkin pipeline with exporter builders #2565 (comment)
  Removed the possibility to set service_name via the Zipkin exporter in favour of leveraging tracer provider
• also removed an unused async_trait in NoopSpanExporter
• slightly simplified with_simple_exporter()
• some of the doc tests were not completely updated after changing the TracerProvider name

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[cijothomas]

Thanks for taking care of leftover cleanups too!

[codecov]

Codecov Report

Attention: Patch coverage is 70.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 79.1%. Comparing base (420416f) to head (00d3223).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...pentelemetry-zipkin/src/exporter/model/endpoint.rs	60.0%	2 Missing ⚠️
opentelemetry-zipkin/src/exporter/mod.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2624   +/-   ##
=====================================
  Coverage   79.0%   79.1%           
=====================================
  Files        119     119           
  Lines      22579   22554   -25     
=====================================
- Hits       17851   17847    -4     
+ Misses      4728    4707   -21     

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