Add option to include Fluent Bit timestamp as auto-generated key

[coderabbitai]

Description

Add an option to include the Fluent Bit timestamp as an auto-generated key in the log events.

Context

This feature request originated from a TODO comment in plugins/out_clp_s3/internal/flush/flush.go during the development of PR #15.

References

• PR: feat: Migrate from IRV1 to KV-IR serializer. #15
• Comment: feat: Migrate from IRV1 to KV-IR serializer. #15 (comment)
• Requested by: @davemarco