Allow overriding the cache-control header when using cached functions

[ronenteva]

Describe the feature

Once cache is used, the cache-control header can't be set manually.

routeRules: {
    '/api/test': {cache: {maxAge: 60}, headers: {'cache-control': 'public, max-age=60, stale-while-revalidate=30'}}
  }

results in cache-control: max-age=60

Additional information

• [ ] Would you be willing to help implement this feature?