fix: Remove mut ref requirement for shutdown LogExporter

[cijothomas]

Redoing https://github.com/open-telemetry/opentelemetry-rust/pull/2634/files

LogExporter shutdown() no longer require mut ref. The component that needs mutability should rely on interior mutability. Most of the exporters already use interior mutability.

Metric already does not require mutable self on shutdown, this makes Logs consistent with that, and later we need to get Traces too.

Also LogProcessor, LogProvider does not require mut ref on shutdown, so this makes exporter aligned as well.

Additionally this also fixes #2770

[codecov]

Codecov Report

Attention: Patch coverage is 16.00000% with 21 lines in your changes missing coverage. Please review.

Project coverage is 79.7%. Comparing base (9d3a507) to head (7a0024e).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-otlp/src/exporter/tonic/logs.rs	0.0%	13 Missing ⚠️
opentelemetry-otlp/src/logs.rs	0.0%	5 Missing ⚠️
opentelemetry-otlp/src/exporter/http/logs.rs	0.0%	1 Missing ⚠️
opentelemetry-sdk/src/logs/export.rs	0.0%	1 Missing ⚠️
opentelemetry-stdout/src/logs/exporter.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #2764     +/-   ##
=======================================
- Coverage   79.7%   79.7%   -0.1%     
=======================================
  Files        123     123             
  Lines      23107   23115      +8     
=======================================
  Hits       18426   18426             
- Misses      4681    4689      +8     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[utpilla]

Looks good for now. The shutdown logic for tonic export can be implemented later.

[cijothomas]

@gruebel Merged this to unblock progress! Please share any feedback on this, and I'll follow up.