Workload Protection reorg Coverage updates

[drichards-87]

What does this PR do? What is the motivation?

This PR reorganizes the Workload Protection Coverage documentation into a reference page and a task-oriented child page.

What changed	Why
Kept Coverage as the reference page and moved its procedural guidance to a new child page, Review and Improve Coverage	Separates information about how Coverage works from the tasks readers perform to assess and improve coverage
Kept the Coverage overview, views, resource lifecycle, statuses, and verdicts on the parent page	Keeps the product reference material together
Organized the child page into five task sections and a recommended review order	Gives readers a sequence to follow while keeping each procedure easy to find
Consolidated the original 10-step review cycle into six steps and ordered the task sections to match	Removes repetition without changing the original progression
Consolidated the Key functionality and Key benefits lists into the page introductions and task guidance	Avoids repeating information already explained by the surrounding content
Added the child page to the navigation and added frontmatter descriptions to both pages	Makes the new structure discoverable and gives both pages distinct metadata

The operational procedures from the original Coverage page are retained. This changes three files and adds one page and one navigation entry.

Merge readiness

• Ready for merge

For Datadog employees:

• ⚠️ Your branch name MUST follow the <name>/<description> convention and include the forward slash (/). If you've already created your PR with an incorrect branch name, please rename your branch and open a fresh PR.
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Additional notes

[github-actions]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/deforest/wp-coverage-reference-and-review/security/workload_protection/inventory/review_improve_coverage

Modified Files

• https://docs-staging.datadoghq.com/deforest/wp-coverage-reference-and-review/security/workload_protection/inventory/