Add enhancements to sitemap route handling

[impactmass]

Resolves NA
Impact: minor
Type: feature+refactor

Changes

During an internal PR review, some refactor + updates were suggested that I'm adding here:

• Switch fetch().then.catch() to async/await
• Bubble up 404 and 500 errors to the error middleware and let them be handled there
• Add Cache-Control header to cache the sitemap. With max-age default of 12 hours.
• Use express route pattern matching

Testing

Testing should be same as the original PR found here #488. You can use reaction's develop branch.

[kieckhafer]

Updates look good