Pull request: 4890-panic-internal-proxy

Updates #4890.

Squashed commit of the following:

commit 20c8f3348125672403c3968b8e08b15eba69347d
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Sep 6 16:55:11 2022 +0300

    dnsforward: imp names

commit 2c21644623c321df46a5c386ec00ca532b7603b6
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Sep 6 16:36:46 2022 +0300

    dnsforward: imp validations; refactor more

commit 221e8c5ebbd0b64e5c554cddb683d116212e5901
Merge: e5f5b76e 58512c3a
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Sep 6 14:57:31 2022 +0300

    Merge branch 'master' into 4890-panic-internal-proxy

commit e5f5b76e3e2b43656af9939a52a9e46e5d9b5a40
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Sep 6 14:51:48 2022 +0300

    dnsforward: fix panic; refactor

internal/dnsforward/testdata/TestDNSForwardHTTP_handleGetConfig.json

@@ -13,7 +13,7 @@
     ],
     "protection_enabled": true,
     "ratelimit": 0,
-    "blocking_mode": "",
+    "blocking_mode": "default",
     "blocking_ipv4": "",
     "blocking_ipv6": "",
     "edns_cs_enabled": false,
@@ -42,7 +42,7 @@
     ],
     "protection_enabled": true,
     "ratelimit": 0,
-    "blocking_mode": "",
+    "blocking_mode": "default",
     "blocking_ipv4": "",
     "blocking_ipv6": "",
     "edns_cs_enabled": false,
@@ -71,7 +71,7 @@
     ],
     "protection_enabled": true,
     "ratelimit": 0,
-    "blocking_mode": "",
+    "blocking_mode": "default",
     "blocking_ipv4": "",
     "blocking_ipv6": "",
     "edns_cs_enabled": false,
@@ -86,4 +86,4 @@
     "use_private_ptr_resolvers": false,
     "local_ptr_upstreams": []
   }
-}
+}