Infer port from protocol if port is not specified and add ability to override hostname in clusters def

[adilhafeez]

If port is not specified in endpoint then port will be inferred from protocol. For example in following arch_config we didn't specify port but the arch gateway inferred port 443 from protocol def,

arch_config.yaml

...
endpoints:
  frankfurther_api:
    endpoint: api.frankfurter.dev
    protocol: https
...

envoy.yaml

...
    - name: frankfurther_api
      connect_timeout: 5s
      type: LOGICAL_DNS
      dns_lookup_family: V4_ONLY
      lb_policy: ROUND_ROBIN
      load_assignment:
        cluster_name: frankfurther_api
        endpoints:
          - lb_endpoints:
              - endpoint:
                  address:
                    socket_address:
                      address: api.frankfurter.dev
                      port_value: 443

                  hostname: api.frankfurter.dev
...