Pull request: 2509 type-safety vol.2

Merge in DNS/adguard-home from 2509-type-safety-vol2 to master

Updates #2509.

Squashed commit of the following:

commit c944e4e0a9949fc894c90b4bc1f739148a67fd9d
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Jan 21 19:36:20 2021 +0300

    all: imp docs

commit e8ac1815c492b0a9434596e35a48755cac2b9f3b
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Wed Jan 20 12:38:48 2021 +0300

    all: imp JSON encoding, decoding

openapi/openapi.yaml

@@ -1452,7 +1452,13 @@
       'type': 'object'
       'description': >
         Information about the latest available version of AdGuard Home.
+      'required':
+      - 'disabled'
       'properties':
+        'disabled':
+          'type': 'boolean'
+          'description': >
+            If true then other fields doesn't appear.
         'new_version':
           'type': 'string'
           'example': 'v0.9'
@@ -1471,7 +1477,10 @@
       'properties':
         'time_units':
           'type': 'string'
-          'description': 'Time units (hours | days)'
+          'enum':
+          - 'hours'
+          - 'days'
+          'description': 'Time units'
           'example': 'hours'
         'num_dns_queries':
           'type': 'integer'
@@ -1988,6 +1997,10 @@
       'properties':
         'flags':
           'type': 'string'
+          'description': >
+            Flags could be any combination of the following values, divided by
+            the "|" character: "up", "broadcast", "loopback", "pointtopoint" and
+            "multicast".
           'example': 'up|broadcast|multicast'
         'hardware_address':
           'type': 'string'