Enable section anchors

What does this MR do?

Enable section anchors and prevent sanitization from removing ids. It also preserves footnote ids.

Resolves #64070 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines (https://docs.gitlab.com/ee/development/merge_request_performance_guidelines.html)
• Style guides

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.