Pull request: all: imp tls cipher selection

Closes #2993.

Squashed commit of the following:

commit 6c521e56de024bf92ab7489ed2289da6bce1f3dc
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Jan 25 21:39:48 2022 +0300

    all: imp tls cipher selection

internal/dnsforward/config.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/AdguardTeam/AdGuardHome/internal/aghtls"
 	"github.com/AdguardTeam/AdGuardHome/internal/filtering"
 	"github.com/AdguardTeam/dnsproxy/proxy"
 	"github.com/AdguardTeam/dnsproxy/upstream"
@@ -426,6 +427,7 @@ func (s *Server) prepareTLS(proxyConfig *proxy.Config) error {
 
 	proxyConfig.TLSConfig = &tls.Config{
 		GetCertificate: s.onGetCertificate,
+		CipherSuites:   aghtls.SaferCipherSuites(),
 		MinVersion:     tls.VersionTLS12,
 	}