feat(*) degraded status in insights

[bartsmykla]

Summary

Adding partially degraded statuses for ServiceInsights and MeshInsights

Examples:

{
 "type": "MeshInsight",
 "name": "default",
 "creationTime": "2020-11-17T08:10:24.886346Z",
 "modificationTime": "2020-11-17T19:21:39.912878Z",
 "lastSync": "2020-11-17T12:21:39.912877Z",
 "dataplanes": {
  "total": 4,
  "online": 2,
  "partially_degraded": 1,
  "offline": 1
 },
 "policies": {
  "Secret": {
   "total": 1
  },
  "TrafficPermission": {
   "total": 1
  },
  "TrafficRoute": {
   "total": 1
  }
 },
 "dpVersions": {
  "kumaDp": {
   "1.0.0-rc2-119-g50e35395": {
    "total": 1,
    "online": 1
   },
   "1.0.4": {
    "total": 2,
    "online": 1,
    "partially_degraded": 1
   },
   "unknown": {
    "total": 1,
    "online": 1
   }
  },
  "envoy": {
   "1.15.0": {
    "total": 2,
    "online": 2
   },
   "unknown": {
    "total": 1,
    "online": 1
   }
  }
 }
}

{
 "type": "ServiceInsight",
 "mesh": "default",
 "name": "backend",
 "creationTime": "2020-10-12T09:40:27.224648+03:00",
 "modificationTime": "2020-10-12T09:40:27.224648+03:00",
 "status": "partially_degraded",
 "dataplanes": {
  "online": 1,
  "offline": 1,
  "total": 3
 }
}

[bartsmykla]

Please wait till I will change the docs as I introduced breaking'ish change for service insights after @lobkovilya pointed mistake in my code

[bartsmykla]

PR with the docs is ready: kumahq/kuma-website#378

[bartsmykla]

Now when it's merged @nickolaev could you also look at: kumahq/kuma-website#378 ?