[Bug]: Track subscription ID as an identity

[VGR-GIT]

Describe the bug

Without putting subscription ID in the metametrics identity, we have no way to correlate data from metametrics with data in our Rewards backend. We need this field in identity and for the RewardsController to populate this after a user opts in. We should also backfill this information since we are making this change after v1 launch. A user could opt out of rewards and then opt in later, so we should upsert on opt-in too.

Expected behavior

No response

Screenshots/Recordings

No response

Steps to reproduce

1. Opt into rewards program
2. We don't associate the subscription_id with the user via traits.

Error messages or log output

Detection stage

In production (default)

Version

7.58

Build type

None

Device

Moto Edge 60 Pro

Operating system

Android, iOS

Additional context

No response

Severity

No response