PLT-6201 Allow tracing to become a true noop

[jhbertra]

• Make tracing a no-op if the OTEL_EXPORTER_OTLP_ENDPOINT env var is not set (this is not standard, but is convenient in our case).
  • No-op means that the global tracer provider is not initialized and that a noopEventBackend is used, so selectors and fields are never held in memory past creation and are not processed into spans and attributes.
• Refactor: consolidate duplicated monad stack into a single module (used in all runtime components, web server, and integration tests).
• Refactor: consolidate tracer initialization to the same place.

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[bwbush]

Nice!