Implement ETW exporter for metrics

[mattbodd]

Fixes #16 Design discussion issue (if applicable) #

Changes

Implements an ETW (Event Tracing for Windows) exporter. This implementation heavily borrows the design patterns of the opentelemetry-user-events metrics exporter and swaps user_event APIs for ETW APIs provided by the tracelogging_dynamic crate.

Merge requirement checklist

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

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 38.38384% with 61 lines in your changes are missing coverage. Please review.

Project coverage is 50.3%. Comparing base (6ede632) to head (36d60bb).

Files	Patch %	Lines
opentelemetry-etw-metrics/src/exporter/mod.rs	0.0%	43 Missing :warning:
opentelemetry-etw-metrics/src/etw/mod.rs	67.8%	18 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #43 +/- ## ======================================= - Coverage 50.6% 50.3% -0.3% ======================================= Files 30 32 +2 Lines 4287 4386 +99 ======================================= + Hits 2171 2209 +38 - Misses 2116 2177 +61 ```

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[lalitb]

This looks awesome. Thanks for contributing :) In the future, we can explore consolidating the functionalities of both user-events and ETW into a single crate (say) opentelemetry-geneva-metrics-exporter, the common serialization logic can be reused, and select the transport protocol—ETW for Windows or user_events for Unix-like systems-- during build based on the platform. Just some thoughts :)

[mattbodd]

This looks awesome. Thanks for contributing :) In the future, we can explore consolidating the functionalities of both user-events and ETW into a single crate (say) opentelemetry-geneva-metrics-exporter, the common serialization logic can be reused, and select the transport protocol—ETW for Windows or user_events for Unix-like systems-- during build based on the platform. Just some thoughts :)

I like this direction and would be happy to follow up with a PR to merge the two functionalities into a single crate. Does that sound ok?

[lalitb]

I like this direction and would be happy to follow up with a PR to merge the two functionalities into a single crate. Does that sound ok?

Yes, let's discuss more internally before finalizing it.