[Documentation] Explain the exporter queue failure scenario

[splunkericl]

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Important (read before submitting)

Is your feature request related to a problem? Please describe. No this is specific to documentation.

Describe the solution you'd like Add a paragraph in exporter helper explaining the failure scenarios:

• if new items can't be added to the queue for whatever reasons, they will be dropped. This means if the memory is full for memory queue and disk is full for persistent queue, the new items will be dropped.
• If the queue is full, new items coming in will be dropped

Additional context As a user of otel collector, I want the failure scenario to be easily documented and found.