Support serving files from AWS S3

[pleshakov]

Integrate this project https://github.com/nginxinc/nginx-s3-gateway/ into NGF, which "provides a working configuration of NGINX configured to act as an authenticating and caching gateway for to AWS S3 or another S3 compatible service. This allows you to proxy a private S3 bucket without requiring users to authenticate to it".

For example, to start serving files from an S3 bucket:

apiVersion: gateway.networking.k8s.io/v1beta1
kind: HTTPRoute
. . .
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /static
    backendRefs:
    - group: gateway.nginx.org/v1
      kind: S3Bucket
      name: my-s3-bucket

where S3Bucket custom resource defines the parameters of accessing the bucket.