Pull request: websvc-config-manager

Merge in DNS/adguard-home from websvc-config-manager to master

Squashed commit of the following:

commit 2143b47c6528030dfe059172888fddf9061e42da
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Oct 4 14:50:47 2022 +0300

    next: add config manager

internal/aghchan/aghchan.go

@@ -0,0 +1,33 @@
+// Package aghchan contains channel utilities.
+package aghchan
+
+import (
+	"fmt"
+	"time"
+)
+
+// Receive returns an error if it cannot receive a value form c before timeout
+// runs out.
+func Receive[T any](c <-chan T, timeout time.Duration) (v T, ok bool, err error) {
+	var zero T
+	timeoutCh := time.After(timeout)
+	select {
+	case <-timeoutCh:
+		// TODO(a.garipov): Consider implementing [errors.Aser] for
+		// os.ErrTimeout.
+		return zero, false, fmt.Errorf("did not receive after %s", timeout)
+	case v, ok = <-c:
+		return v, ok, nil
+	}
+}
+
+// MustReceive panics if it cannot receive a value form c before timeout runs
+// out.
+func MustReceive[T any](c <-chan T, timeout time.Duration) (v T, ok bool) {
+	v, ok, err := Receive(c, timeout)
+	if err != nil {
+		panic(err)
+	}
+
+	return v, ok
+}