[sitecore-jss-nextjs] Refactor RedirectsMiddleware for Better Extensibility

[ah100101]

This PR refactors the RedirectsMiddleware class to improve its extensibility and maintainability by:

1. Extracting the main redirect processing logic into a protected method
2. Making getExistsRedirect protected to allow override in derived classes

• This PR follows the Contribution Guide
• Changelog updated

Description / Motivation

Extending RedirectsMiddleware or MiddlewareBase currently requires re-implementing the entire handler. Changing getExistsRedirect to a protected method and encapsulating the handler will make it easier to extend RedirectsMiddleware and add optimizations like caching or logic to bypass fetches to Sitecore under certain criteria.

This PR makes the following changes:

1. Creates new protected method processRedirectRequest that encapsulates the core redirect logic
2. Changed getExistsRedirect access modifier from private to protected
3. Simplified the handler to delegate to processRedirectRequest

Testing Details

Existing functionality in RedirectsMiddleware remains the same. These changes were tested in both development and production deployed applications on Vercel.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

[yavorsk]

Solid work, thanks for the contribution!
I added this in our backlog for review and prioritization.