Support referencing/overriding the traceSampled field

[rpysz]

Describe the bug
Issue similar to #1483. I would like to have a possibility to propagate "traceSampled" same way as "trace" and "spanId" (or rather have a possibility to always set this field to boolean true, not string "true" - Google API ignores stringified values of "traceSampled" field).

Expected behavior
'traceSampled' field properly propagated to Google Cloud Logging as boolean type

Environment:
VM distro / OS: Red Hat Enterprise Linux 8 (version 8.8)
Ops Agent version: 2.44.0

[jefferbrecht]

As an alternative, would it be acceptable if the Ops Agent were to set traceSampled=true automatically whenever exporting a log that has trace or spanId? Or is there some other use case where you would need to be able to manually toggle traceSampled independently?

[rpysz]

@jefferbrecht For my solution, always setting traceSampled=true is sufficient.