Fill "network" section in m.bridge state key

[MurzNN]

Seems "network" section of MSC2346 isn't filled by mx-puppet-slack bridge.

Here is example of state key:

{
  "type": "uk.half-shot.bridge",
  "sender": "@_slackpuppet_bot:ru-matrix.org",
  "content": {
    "bridgebot": "@_slackpuppet_bot:ru-matrix.org",
    "creator": "@murz:ru-matrix.org",
    "protocol": {
      "id": "slack",
      "displayname": "Slack",
      "external_url": "https://slack.com"
    },
    "channel": {
      "id": "_t06_g_x3_j_t_s=2d_c6_s_q_m2_j94",
      "displayname": "views - Drupal",
      "avatar_url": "mxc://ru-matrix.org/YVtqrjOMufllpWmupyUsuYuy"
    }
  },
  "state_key": "de.sorunome.mx-puppet-bridge://slack/_t06_g_x3_j_t_s%3D2d_c6_s_q_m2_j94",
  "origin_server_ts": 1605367810798,
  "unsigned": {
    "age": 4989531134
  },
  "event_id": "[censored]",
  "room_id": "[censored]:ru-matrix.org"
}

Via this info we can't understand with which Slack workspace this room is bridge.

Will be good to fill "network" section with suitable data from Slack workspace:

        "network": {
            "id": "slack workspace id",
            "displayname": "slack workspace display name",
            "avatar_url": "slack workspace avatar",
            "external_url": "slack workspace frontpage"
        },