example_otlp_grpc_log logs epoch time which could be misleading

[ThomsonTan]

Describe your environment

example_otlp_grpc_log logs an entry with epoch timestamp, which may not be useful as real world example, because the timestamp could be rejected by logs processing backend.

Steps to reproduce
Run example_tolp_grpc_log and observe the generated log timestamp.

What is the expected behavior?
What did you expect to see? 0

What is the actual behavior?
What did you see instead? The current timestamp.