Prom2teams parses only the first received alarm

[jnogol]

A JSON sent by Prometheus could have this format, with more than one alert:

{
  "receiver": "test_webhook",
  "status": "resolved",
  "alerts": [
    {
      "status": "resolved",
      "labels": {
        "alertname": "DiskSpace",
        "device": "rootfs",
        "fstype": "rootfs",
        "instance": "cs30.evilcorp",
        "job": "fsociety",
        "mountpoint": "/",
        "severity": "severe"
      },
      "annotations": {
        "description": "disk usage 73% on rootfs device",
        "summary": "Disk usage alert on CS30.evilcorp"
      },
      "startsAt": "2015-05-09T07:01:37.803Z",
      "endsAt": "2015-05-09T07:08:37.818278068Z",
      "generatorURL": "my.prometheusserver.url"
    },
    {
      "status": "resolved",
      "labels": {
        "alertname": "DiskSpace",
        "device": "/dev/mapper/vg1-lv1",
        "fstype": "ext4",
        "instance": "cs30.evilcorp",
        "job": "fsociety",
        "mountpoint": "/whiterose",
        "severity": "severe"
      },
      "annotations": {
        "description": "disk usage 52% on /dev/mapper/vg1-lv1 device",
        "summary": "Disk usage alert on cs30.evilcorp"
      },
      "startsAt": "2015-05-09T07:01:37.803Z",
      "endsAt": "2015-05-09T07:08:37.818278068Z",
      "generatorURL": "my.prometheus.url"
    }
  ],
  "groupLabels": {
    "alertname": "DiskSpace",
    "instance": "cs30.evilcorp",
    "severity": "severe"
  },
  "commonLabels": {
    "alertname": "DiskSpace",
    "instance": "cs30.evilcorp",
    "job": "fsociety",
    "severity": "severe"
  },
  "commonAnnotations": {
    "summary": "Disk usage alert on cs30.evilcorp"
  },
  "externalURL": "my.prometheusalertmanager.url",
  "version": "4",
  "groupKey": "{}/{severity=~\"^(?:severe)$\"}:{alertname=\"DiskSpace\", instance=\"cs30.evilcorp\", severity=\"severe\"}"
}

Problem is that prom2teams, in this line https://github.com/idealista/prom2teams/blob/master/prom2teams/message/parser.py#L13 (and I take the blame for that one, didn't expect Prometheus to send more than one alert per JSON) just parses the first alarm.

So parser.py has to be changed, parse more than one alert and then prom2teams should send these alarms (changes needed as well in server.py, I think)