Pull request: all: update go and backend tools

Closes #2576.
Updates #2275.
Updates #2419.
Updates #2443.

Squashed commit of the following:

commit b1a4809ada298d675de12740051ba26fb9945957
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri May 21 14:01:40 2021 +0300

    all: add --local-frontend, upd docker

commit 619ee7c82f27e3405753003dbec556ffb056d025
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu May 20 15:02:33 2021 +0300

    bamboo-specs: bump docker version

commit 5c2b2fbce80afdcc81fd0cb83674dc3d64facbf1
Merge: 6536b32d 9c60aef6
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu May 20 15:01:47 2021 +0300

    Merge branch 'master' into 2275-upd-go

commit 6536b32dd4580425f7dedde6765463a79b9bd699
Merge: 9bb32bc4 6f7fd33a
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed May 19 20:38:48 2021 +0300

    Merge branch 'master' into 2275-upd-go

commit 9bb32bc4c0ac0f3a97195adc75359e48c9c58897
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed May 19 18:48:50 2021 +0300

    all: fix build, imp err handling

commit 6868eac7f7d2980fb706881f53e72afe5f7c3447
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed May 19 18:09:32 2021 +0300

    all: fix github lint

commit ebbb9c55f32fbd57e34e8b161016aa6b291c097c
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed May 19 17:36:56 2021 +0300

    all: update go and backend tools

internal/dnsforward/config.go

@@ -5,9 +5,9 @@ import (
 	"crypto/x509"
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"net"
 	"net/http"
+	"os"
 	"sort"
 
 	"github.com/AdguardTeam/AdGuardHome/internal/aghstrings"
@@ -275,7 +275,7 @@ func (s *Server) prepareUpstreamSettings() error {
 	// Load upstreams either from the file, or from the settings
 	var upstreams []string
 	if s.conf.UpstreamDNSFileName != "" {
-		data, err := ioutil.ReadFile(s.conf.UpstreamDNSFileName)
+		data, err := os.ReadFile(s.conf.UpstreamDNSFileName)
 		if err != nil {
 			return err
 		}

internal/dnsforward/dnsforward_test.go

@@ -9,7 +9,6 @@ import (
 	"crypto/x509/pkix"
 	"encoding/pem"
 	"fmt"
-	"io/ioutil"
 	"math/big"
 	"net"
 	"os"
@@ -1082,9 +1081,8 @@ func TestPTRResponseFromHosts(t *testing.T) {
 	}
 
 	// Prepare test hosts file.
-	hf, err := ioutil.TempFile("", "")
+	hf, err := os.CreateTemp("", "")
 	require.NoError(t, err)
-
 	t.Cleanup(func() {
 		assert.NoError(t, hf.Close())
 		assert.NoError(t, os.Remove(hf.Name()))

internal/dnsforward/http_test.go

@@ -3,7 +3,7 @@ package dnsforward
 import (
 	"bytes"
 	"encoding/json"
-	"io/ioutil"
+	"io"
 	"net"
 	"net/http"
 	"net/http/httptest"
@@ -207,7 +207,7 @@ func TestDNSForwardHTTTP_handleSetConfig(t *testing.T) {
 				s.conf = defaultConf
 			})
 
-			rBody := ioutil.NopCloser(bytes.NewReader(caseData.Req))
+			rBody := io.NopCloser(bytes.NewReader(caseData.Req))
 			var r *http.Request
 			r, err = http.NewRequest(http.MethodPost, "http://example.com", rBody)
 			require.Nil(t, err)

internal/dnsforward/ipset_linux.go

@@ -1,5 +1,7 @@
 // +build linux
 
+//go:build linux
+
 package dnsforward
 
 import (

internal/dnsforward/ipset_others.go

@@ -1,5 +1,7 @@
 // +build !linux
 
+//go:build !linux
+
 package dnsforward
 
 import (