chore(nimbus-sdk): move enrollment status to separate ping

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• Breaking changes: This PR follows our breaking change policy
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    • This PR has no breaking API changes, or
    • There are corresponding PRs for our consumer applications that resolve the breaking changes and have been approved
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There are corresponding PRs for our consumer applications that resolve the breaking changes and have been approved

This change does not break Fenix, because the changed API is implemented within this repo.
For firefox-ios, the fix is mozilla-mobile/firefox-ios#32150