Update Report Internals section to reflect unified EphemeralReport type

[maheshcodes12]

Related issue

Closes #1642

Proposed Changes

This PR updates the "Report Internals" section of the Kyverno documentation to reflect changes introduced in Kyverno v1.12 PR #9537, where the separate AdmissionReport/ClusterAdmissionReport and BackgroundReport/ClusterBackgroundReport resources were unified into the EphemeralReport/ClusterEphemeralReport types. These unified resources now cover both admission and background scan results.

This update ensures the documentation matches the current behavior and data model in Kyverno starting from v1.12.

Checklist

• [x] I have read the contributing guidelines.
• [x] I have inspected the website preview for accuracy.
• [x] I have signed off my issue.

[maheshcodes12]

I discovered that this issue is related to another one. Resolving this will also close that issue. @MariamFahmy98 Can you please review new changes.