Treat PartialSuccess as Success

[jmacd]

Description: Changes the treatment of PartialSuccess, making them successful and logging a warning instead of returning an error to the caller. These responses are meant to convey successful receipt of valid data which could not be accepted for other reasons, specifically to cover situations where the OpenTelemetry SDK and Collector have done nothing wrong, specifically to avoid retries. While the existing OTLP exporter returns a permanent error (also avoids retries), it makes the situation look like a total failure when in fact it is more nuanced.

As discussed in the tracking issue, it is a lot of work to propagate these "partial" successes backwards in a pipeline, so the appropriate simple way to handle these items is to return success.

In this PR, we log a warning. In a future PR, (IMO) as discussed in open-telemetry/oteps#238, we should count the spans/metrics/logs that are rejected in this way using a dedicated outcome label.

Link to tracking Issue:
Part of #9243

Testing: Tests for the "partial success" warning have been added.

Documentation: PartialSuccess behavior was not documented. Given the level of detail in the README, it feels appropriate to continue not documenting, otherwise lots of new details should be added.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f5a7315) 0.00% compared to head (073ed55) 90.47%.

❗ Current head 073ed55 differs from pull request most recent head a14666b. Consider uploading reports for the commit a14666b to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##           main    #9260       +/-   ##
=========================================
+ Coverage      0   90.47%   +90.47%     
=========================================
  Files         0      344      +344     
  Lines         0    18042    +18042     
=========================================
+ Hits          0    16323    +16323     
- Misses        0     1390     +1390     
- Partials      0      329      +329     

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[jmacd]

(Realize I need to fix the otlphttpexporter too!)

[TylerHelmuth]

This aligns with my understanding of https://github.com/open-telemetry/opentelemetry-proto/blob/main/docs/specification.md#partial-success and https://github.com/open-telemetry/opentelemetry-proto/blob/main/docs/specification.md#partial-success-1

[jmacd]

Reviewers, this is ready for review.

[jmacd]

Test failure looks unrelated:

Error: ./factory_test.go:142:3: unknown field GRPCClientSettings in struct literal of type otlpexporter.Config
Error: ./traces_test.go:39:3: unknown field GRPCClientSettings in struct literal of type otlpexporter.Config