Pull request: 3136 show default resolvers

Merge in DNS/adguard-home from 3136-show-default to master

Closes #3136.

Squashed commit of the following:

commit add09a772dddcccd404056e7649c2d3350a79fec
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Jun 1 11:11:24 2021 +0300

    openapi: fix typo

commit 69e402c49318d53a0d03b81207644d9fb04a139a
Merge: 76e8492c e17e1f20
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Jun 1 11:09:51 2021 +0300

    Merge branch 'master' into 3136-show-default

commit 76e8492c8da679e204ceb7a77f1c6f73a2488040
Author: Ildar Kamalov <ik@adguard.com>
Date:   Tue Jun 1 10:55:09 2021 +0300

    client: check upstreams

commit 05fe6ea196a1ed9386eec25dbfbe22779fe7bcfd
Author: Vlad <v.abdulmyanov@adguard.com>
Date:   Mon May 31 19:23:35 2021 +0300

    add defaul resolvers line

commit 8d63c7df9947c9588478d1173834b42569fd8951
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon May 31 11:56:08 2021 +0300

    all: imp changelog

commit e3912e3b20eca9dcf90ddddaa5edb54d1e0cfe6e
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri May 28 20:23:05 2021 +0300

    all: add local ptr resolvers addresses output

openapi/CHANGELOG.md

@@ -4,6 +4,12 @@
 
 ## v0.107: API changes
 
+### The new field `"default_local_ptr_upstreams"` in `GET /control/dns_info`
+
+* The new optional field `"default_local_ptr_upstreams"` is the list of IP
+  addresses AdGuard Home would use by default to resolve PTR request for
+  addresses from locally-served networks.
+
 ### The field `"use_private_ptr_resolvers"` in DNS configuration
 
 * The new optional field  `"use_private_ptr_resolvers"` of `"DNSConfig"`

openapi/openapi.yaml

@@ -69,7 +69,17 @@
           'content':
             'application/json':
               'schema':
-                '$ref': '#/components/schemas/DNSConfig'
+                'allOf':
+                - '$ref': '#/components/schemas/DNSConfig'
+                - 'type': 'object'
+                  'properties':
+                    'default_local_ptr_upstreams':
+                      'type': 'array'
+                      'items':
+                        'type': 'string'
+                      'example':
+                      - '192.168.168.192'
+                      - '10.0.0.10'
   '/dns_config':
     'post':
       'tags':