Collect coldstart FAAS metadata for function logs

[lahsivjar]

Is your feature request related to a problem? Please describe.
Currently, function logs only collect request ID and ARN as FAAS metadata. Investigate collection of coldstart metadata.

Describe the solution you'd like
Based on the lifecycle of events and the extension, value of coldstart can be deduced.

Describe alternatives you've considered
N/A

Additional context
#303 (comment)