[FEATURE] Enhancements in Message statistics

[dobromirdobrev]

Is your feature request related to a problem? Please describe.

1. The Admin app has to show message subject in the UI
2. The admin app has to show a list of users which are message recipients
3. The Admin app has to show a list of users who read the message

Describe the solution you'd like

1. The GET API /api/admin/messages/stats/source/{source} to return the title / subject in the json response. Possible response:

  {
    "date_created": "2023-04-05T12:37:06.899Z",
    "title": "Test message title.",
    "message": "Test message body.",
    "read_count": 1,
    "recipients_count": 1,
    "sent_by": {
      "account_id": "df595ef9-3e2b-11ec-bd94-0a58a9feac02",
      "name": "Dobromir Dobrev"
    },
    "time": "2023-04-05T12:37:06.899Z"
  }

2. A new GET API for retrieving the recipient account list with possibility for paging. Possible solution:
   GET /api/admin/messages/stats/recipients/{message_id}?offset=0&limit=20

Response:

[
  {
    "id": "55555",
    "profile": {
      "first_name": "Dobromir",
      "last_name": "Dobrev"
    }
  }
]

This proposal will require the message id to be returned in the json response from point 1.

3. A new GET API for retrieving the recipient account list who read the message with possibility for paging. Possible solution:
   GET /api/admin/messages/stats/read/{message_id}?offset=0&limit=20

Response:

[
  {
    "id": "55555",
    "profile": {
      "first_name": "Dobromir",
      "last_name": "Dobrev"
    }
  }
]

This proposal will require the message id to be returned in the json response from point 1.

Note: These are just proposed solution. Adjust them as needed in the context of the BB implementation.

Additional context
This issue is related to https://github.com/rokwire/illinois_admin/issues/123