[dev] Include expose settings in show application output

[achilleasa]

Description of change

This PR updates the juju show application command so that it includes information about exposed endpoints.

QA steps

# Deploy the following bundle:
$ cat bundle.yaml
series: bionic
applications:
  apache2:
    charm: cs:apache2-35
    num_units: 1
    to:
    - "0"
machines:
  "0": {}
--- # overlay.yaml
applications:
  apache2:
    exposed-endpoints:
      "":
        expose-to-cidrs:
        - 0.0.0.0/0
      website:
        expose-to-cidrs:
        - 10.0.0.0/24

$ juju deploy ./bundle.yaml
$ juju show-application apache2
apache2:
  charm: apache2
  series: bionic
  principal: true
  exposed: true
  exposed-endpoints:
    "":
      expose-to-cidrs:
      - 0.0.0.0/0
    website:
      expose-to-spaces:
      - alpha
      expose-to-cidrs:
      - 10.0.0.0/24
  remote: false
  endpoint-bindings:
    "": alpha
    apache-website: alpha
    balancer: alpha
    local-monitors: alpha
    logging: alpha
    logs: alpha
    nrpe-external-master: alpha
    reverseproxy: alpha
    vhost-config: alpha
    website: alpha
    website-cache: alpha

$ juju show-application apache2 --format json | jq .
{
  "apache2": {
    "charm": "apache2",
    "series": "bionic",
    "constraints": {},
    "principal": true,
    "exposed": true,
    "exposed-endpoints": {
      "": {
        "expose-to-cidrs": [
          "0.0.0.0/0"
        ]
      },
      "website": {
        "expose-to-spaces": [
          "alpha"
        ],
        "expose-to-cidrs": [
          "10.0.0.0/24"
        ]
      }
    },
    "remote": false,
    "endpoint-bindings": {
      "": "alpha",
      "apache-website": "alpha",
      "balancer": "alpha",
      "local-monitors": "alpha",
      "logging": "alpha",
      "logs": "alpha",
      "nrpe-external-master": "alpha",
      "reverseproxy": "alpha",
      "vhost-config": "alpha",
      "website": "alpha",
      "website-cache": "alpha"
    }
  }
}

[achilleasa]

$$merge$$