Add ObservedTimeUnixNano Fallback for Missing TimeUnixNano Field

[bastonta]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

I'm encountering an issue where the log timestamp defaults to "1/1/1970 0:00:00.000 AM" whenever the TimeUnixNano field is not set.

Describe the solution you'd like

Would it be possible to:

• Add the ObservedTimestamp property to be displayed on the UI?
• Provide a fallback mechanism where, if TimeUnixNano is not populated, the ObservedTimeUnixNano field is used instead?

Additional context

The ObservedTimeUnixNano field is described in the OpenTelemetry specification:
ObservedTimestamp Documentation.

The TimeUnixNano field is currently used in the following file:
OtlpLogEntry.cs#L29.