Pull request: websvc: add system info

Merge in DNS/adguard-home from websvc-system-info to master

Squashed commit of the following:

commit 333aaa0602da254e25e0262a10080bf44a3718a7
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu May 12 16:32:32 2022 +0300

    websvc: fmt

commit d8a35bf71dcc59fdd595494e5b220e3d24516728
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu May 12 16:10:11 2022 +0300

    websvc: refactor, imp tests

commit dfeb24f3f35513bf51323d3ab6f717f582a1defc
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed May 11 20:52:02 2022 +0300

    websvc: add system info

openapi/v1.yaml

@@ -3393,11 +3393,17 @@
       'description': >
         Information about the AdGuard Home server.
       'example':
+        'arch': 'amd64'
         'channel': 'release'
-        'new_version': 'v0.106.1'
+        'new_version': 'v0.108.1'
+        'os': 'linux'
         'start': 1614345496000
-        'version': 'v0.106.0'
+        'version': 'v0.108.0'
       'properties':
+        'arch':
+          'description': >
+            CPU architecture.
+          'type': 'string'
         'channel':
           '$ref': '#/components/schemas/Channel'
         'new_version':
@@ -3405,6 +3411,10 @@
             New available version of AdGuard Home to which the server can be
             updated, if any.  If there are none, this field is absent.
           'type': 'string'
+        'os':
+          'description': >
+            Operating system type.
+          'type': 'string'
         'start':
           'description': >
             Unix time at which AdGuard Home started working, in milliseconds.
@@ -3415,7 +3425,9 @@
             Current AdGuard Home version.
           'type': 'string'
       'required':
+      - 'arch'
       - 'channel'
+      - 'os'
       - 'start'
       - 'version'
       'type': 'object'