Support HTTP paths/routes configuration

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**Tell us about your request**
Add simple reverse proxy URL filter functionality to allow/deny some paths, possibly with a custom response.

Example:

- Allow: `/api/v2/**`
- Return 404: `/actuator/health`

Essentially, incorporate the equivalent of ELB routing rules to expand the customization of the service.

**Describe alternatives you've considered**
Today everything needs to be managed inside the app, and adding a load balancer in front of App Runner doesn't look like a good approach.

No repository files, tests, or implementation entry points are named. Start by reviewing the requested allow/deny examples and the proposed ELB-routing equivalent; done means App Runner can configure path filters and a custom 404 response as specified.

Written by the indexing model from the issue text.