Replace deprecated ioutil with io and os (#20776)

* Replace ioutil with io and os

* Replace ioutil in utils/file.go

* Minor fix to tests and excluded files

Co-authored-by: Tim Scheuermann <tim.scheuermann@mattermost.com>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

services/httpservice/client_test.go

@@ -6,7 +6,7 @@ package httpservice
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net"
 	"net/http"
 	"net/http/httptest"
@@ -108,7 +108,7 @@ func TestHTTPClientWithProxy(t *testing.T) {
 	require.NoError(t, err)
 	defer resp.Body.Close()
 
-	body, err := ioutil.ReadAll(resp.Body)
+	body, err := io.ReadAll(resp.Body)
 	require.NoError(t, err)
 	require.Equal(t, "proxy", string(body))
 }