Add support for server-snippet and configuration-snippet annotations

[kelkawi-a]

Enhancement Proposal

These snippets can be used to further customize the nginx ingress. An example can be found below:

  annotations:
    nginx.ingress.kubernetes.io/configuration-snippet: |
      keepalive_timeout 600s;
    nginx.ingress.kubernetes.io/server-snippet: |
      client_header_timeout 3600s;
      client_body_timeout 3600s;