Pull request: 4925-refactor-tls-vol-1

Merge in DNS/adguard-home from 4925-refactor-tls-vol-1 to master

Squashed commit of the following:

commit ad87b2e93183b28f2e38666cc4267fa8dfd1cca0
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Oct 14 18:49:22 2022 +0300

    all: refactor tls, vol. 1

    Co-Authored-By: Rahul Somasundaram <Rahul.Somasundaram@checkpt.com>

internal/aghtls/root.go

@@ -0,0 +1,14 @@
+package aghtls
+
+import (
+	"crypto/x509"
+)
+
+// SystemRootCAs tries to load root certificates from the operating system.  It
+// returns nil in case nothing is found so that Go' crypto/x509 can use its
+// default algorithm to find system root CA list.
+//
+// See https://github.com/AdguardTeam/AdGuardHome/issues/1311.
+func SystemRootCAs() (roots *x509.CertPool) {
+	return rootCAs()
+}