Pull request 1897: nextapi-write-conf

Squashed commit of the following:

commit 72f25ffe73d6b8216b01e590fba66fb5f6944113
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Jun 28 21:29:04 2023 +0300

    next: add conf writing, validation

internal/next/cmd/signal.go

@@ -7,7 +7,6 @@ import (
 
 	"github.com/AdguardTeam/AdGuardHome/internal/aghos"
 	"github.com/AdguardTeam/AdGuardHome/internal/next/agh"
-	"github.com/AdguardTeam/AdGuardHome/internal/next/configmgr"
 	"github.com/AdguardTeam/golibs/log"
 )
 
@@ -63,7 +62,7 @@ func (h *signalHandler) reconfigure() {
 	// reconfigured without the full shutdown, and the error handling is
 	// currently not the best.
 
-	confMgr, err := configmgr.New(h.confFile, h.frontend, h.start)
+	confMgr, err := newConfigMgr(h.confFile, h.frontend, h.start)
 	check(err)
 
 	web := confMgr.Web()