Clean-up middleware

[paescuj]

Scope

• Some middleware were unnecessarily async - these have been updated now, which might lead to a tiny performance improvement
• Consistent naming, named exports
• Prevent shadowing of async middleware return type with RequestHandler type
• return next() instead of next() at end of middleware for sake of consistency
• Move "handlers" to respective places, keep global "middlewares" only in /middleware folder
• Move rateLimiterGlobal and rateLimiterIp instances to own files (use... pattern)
• Remove checks in cors, rateLimiterGlobal and rateLimiterIp middlewares as already in app.ts
• A few smaller enhancements

Potential Risks / Drawbacks

No logical changes

Review Notes / Questions

None