chore: add configurator method docs

[RedZapdos123]

Style/DocumentationMethod reports 5 informational offenses in sdk/lib/opentelemetry/sdk/configurator.rb for undocumented methods in NoopTextMapPropagator and the Configurator getters.

This PR adds minimal method documentation comments for those methods and keeps the change scoped to a single file. It does not change behavior.

[kaylareopelle]

One concern related to error_handler. Everything else looks good to go! Thank you!

[RedZapdos123]

Looked into the failing opentelemetry-sdk / ubuntu-24.04 check. It seems to be a separate flaky test in sdk/test/opentelemetry/sdk/trace/export/batch_span_processor_test.rb, not a regression from this PR.

Reproduced it under JRuby. The reports consistent label keys example can race with the worker thread so the queue overflow path is sometimes skipped and only one otel.bsp.dropped_spans metric entry is recorded. I opened #2321 to make that example deterministic by setting start_thread_on_boot: false.