[Reporting] Forward-port config deprecation fixes from 7.x

[tsullivan]

Summary

Forward port selected fixes of reporting config deprecation from:

• [Reporting] lower roles.enabled deprecation to warning-level #114204
• [Reporting] fix the deprecation text on removal of xpack.reporting.index #114219

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 1203ca4
• Storybooks Preview

Metrics [docs]

✅ unchanged

History

• 💚 Build #160773 succeeded 7142ba2

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[elasticmachine]

Pinging @elastic/kibana-reporting-services (Team:Reporting Services)

[tsullivan]

These changes have already been reviewed in:

• [Reporting] lower roles.enabled deprecation to warning-level #114204
• [Reporting] fix the deprecation text on removal of xpack.reporting.index #114219

In this branch, the changes also include the removal of the xpack.reporting.index deprecation warning - it is in regards to code that has been removed.