feat: add an example for creating a geofence based on a Circle-Area

[maxl2287]

What type of PR is this?

Add one of the following kinds:

• enhancement

What this PR does / why we need it:

Adds a valid example for POST /subscriptions where the area-object is filled.

{
  "webhook": {
    "notificationUrl": "https://application-server.com",
    "notificationAuthToken": "c8974e592c2fa383d4a3960714"
  },
  "subscriptionDetail": {
    "device": {
      "phoneNumber": 4912345678912,
      "networkAccessIdentifier": "123456789@domain.com",
      "ipv4Address": {
        "publicAddress": "84.125.93.10",
        "publicPort": 59765
      },
      "ipv6Address": "2001:db8:85a3:8d3:1319:8a2e:370:7344"
    },
    "area": {
      "areaType": "CIRCLE",
      "center": {
        "latitude": 50.735851,
        "longitude": 7.10066
      },
      "radius": 2000
    },
    "type": "org.camaraproject.geofencing.v0.area-entered"
  },
  "subscriptionExpireTime": "2024-03-22T05:40:58.469Z"
}

Which issue(s) this PR fixes:

Fixes #164

[maxl2287]

@bigludo7 @jlurien I was unsure about the version, because it's more a fix then a feature, but I am using currently 0.2.0-wip. wdyt?

Best regards Max

[maxl2287]

I have updated the description / header to be an enhancement.

[bigludo7]

Thanks As we fix the example should we keep phoneNumber, ipv4, ipv6 and networkAccessIdentifier all valued? It could provide the (wrong) interpretation that all these must be valued.

For me only providing the phoneNumber for an example is fine.