Pull request 2149: 6711 watch hosts

Updates #6711.

Squashed commit of the following:

commit 3ddfe809f76325c2d4cda0715a7bcc15e76a2388
Merge: 185957cd0 d338451fa
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Feb 13 13:01:30 2024 +0300

    Merge branch 'master' into 6711-watch-hosts

commit 185957cd01516e5955e388108615e6f131d6ad71
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Fri Feb 9 18:11:41 2024 +0300

    aghos: imp docs

commit 3afbbcbb7ab6cc60c7c40ef8acd5b3ddf52cb3d1
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Fri Feb 9 15:40:02 2024 +0300

    all: upd golibs, imp fswatcher

internal/dnsforward/http_test.go

@@ -418,6 +418,7 @@ func TestServer_HandleTestUpstreamDNS(t *testing.T) {
 			},
 		},
 		&aghtest.FSWatcher{
+			OnStart:  func() (_ error) { panic("not implemented") },
 			OnEvents: func() (e <-chan struct{}) { return nil },
 			OnAdd:    func(_ string) (err error) { return nil },
 			OnClose:  func() (err error) { return nil },