Use caddy's certmagic library for extensible/robust ACME handling (#14177)

* use certmagic for more extensible/robust ACME cert handling

* accept TOS based on config option

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lauris BH <lauris@nix.lv>

vendor/golang.org/x/net/ipv4/icmp_stub.go

@@ -0,0 +1,25 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !linux
+
+package ipv4
+
+const sizeofICMPFilter = 0x0
+
+type icmpFilter struct {
+}
+
+func (f *icmpFilter) accept(typ ICMPType) {
+}
+
+func (f *icmpFilter) block(typ ICMPType) {
+}
+
+func (f *icmpFilter) setAll(block bool) {
+}
+
+func (f *icmpFilter) willBlock(typ ICMPType) bool {
+	return false
+}