fix(nimbus): populate config_slug on mobile

[moibra05]

Added a proper value for conflict_slug when constructing the EnrollmentStatusExtraDef taken by pulling out the actual feature slug which caused the conflict

Pull Request checklist

• Breaking changes: This PR follows our breaking change policy
  • This PR follows the breaking change policy:
    • 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
• Quality: This PR builds and tests run cleanly
  • Note:
    • For changes that need extra cross-platform testing, consider adding [ci full] to the PR title.
    • If this pull request includes a breaking change, consider cutting a new release after merging.
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry in CHANGELOG.md or an explanation of why it does not need one
  • Any breaking changes to Swift or Kotlin binding APIs are noted explicitly
• Dependencies: This PR follows our dependency management guidelines
  • Any new dependencies are accompanied by a summary of the due diligence applied in selecting them.

[freshstrangemusic]

All changes to types that are serialized to the database require tests and (in this case) a migration

[freshstrangemusic]

There is a line above this that says:

// ⚠️ Warning : Do not change the JSON data used by this test. ⚠️

This test as written is not very useful. It should instead be re-written (with the original JSON) to

• write the original JSON to the database
• set the database version to v3
• load the database
• read the enrollment for "secure-gold"
• validate that it parses with conflict_slug == None