Migrate "Not found errors (404)" module to V4 report

[ChristopherJennings]

Overview

We should migrate the Not found errors (404) module to the new V4 report format.

Definition of done

• Code and Scripts are ported to KenticoInspector.Reports project in a dedicated folder for the report.
• Scripts are referenced via constants in a static class.
• Scripts are refactored to return simple results that are mappable to simple classes.
• Report logic is covered by unit test for a clean result
• Report logic is covered by unit tests for all known dirty results
• Useful, non-specific logic is abstracted to services or helpers.

Note: The Class/Table Validation report (and it's tests) is a good, simple example of the main concepts.

Additional Details

• New name: Page not found error analysis
• Tags: Health, Information