Break redirect code into helpers and validations

What does this MR do?

Restructure some of the logic in redirects.go into two separate files: helpers.go and validations.go.

This MR also adds some tests for the existing normalizePath function.

Why?

This restructuring is in preparation for the changes being made in !458 (merged), where a significant amount of new logic will be added to both helpers.go and validations.go.

TODO

• Added the Changelog (e.g. Changelog: feature) trailer to the commits that need to be included in the changelog
• Added unit tests (if required)
• Added acceptance tests (if required)
• Documentation (if required)
• Code review guidelines
• Go Style guidelines