Update segment to send "common fields"

[unn]

Describe the bug
Our custom OS, ddev_version, and instrumentation_user should be updated to leverage common fields, see links below.

Expected behavior
Our custom implementation of OS should be replaced by the common field os.
Our custom implementation of ddev_version should be replaced by the common field app version.
Our custom implementation of instrumentation_user should be replaced with a common trait like name or a custom trait.

Additional context
https://segment.com/docs/spec/common/#context
https://github.com/segmentio/analytics-go/blob/v3.0/context.go#L95 
https://github.com/segmentio/analytics-go/blob/v3.0/context.go#L39 

[rfay]

While doing this:

• Consider moving the global_config.yaml specification of a known user to a specific field of its own.