chore!(amneziawg): refactor to be separate from wireguard

- amneziawg is now a VPN protocol and no longer a Wireguard implementation
- Use it with VPN_TYPE=amneziawg
- document AMNEZIAWG_* options in Dockerfile
- document amneziawg support in readme
- separate amneziawg settings and code from wireguard
- re-use code from wireguard whenever possible

internal/wireguard/cleanup.go

@@ -1,63 +0,0 @@
-package wireguard
-
-import "sort"
-
-type closer struct {
-	operation string
-	step      step
-	close     func() error
-	closed    bool
-}
-
-type closers []closer
-
-func (c *closers) add(operation string, step step,
-	closeFunc func() error,
-) {
-	closer := closer{
-		operation: operation,
-		step:      step,
-		close:     closeFunc,
-	}
-	*c = append(*c, closer)
-}
-
-func (c *closers) cleanup(logger Logger) {
-	closers := *c
-
-	sort.Slice(closers, func(i, j int) bool {
-		return closers[i].step < closers[j].step
-	})
-
-	for i, closer := range closers {
-		if closer.closed {
-			continue
-		}
-		closers[i].closed = true
-		logger.Debug(closer.operation + "...")
-		err := closer.close()
-		if err != nil {
-			logger.Error("failed " + closer.operation + ": " + err.Error())
-		}
-	}
-}
-
-type step int
-
-const (
-	// stepOne closes the wireguard controller client,
-	// and removes the IP rule.
-	stepOne step = iota
-	// stepTwo closes the UAPI listener.
-	stepTwo
-	// stepThree closes the UAPI file.
-	stepThree
-	// stepFour shuts down the Wireguard link.
-	stepFour
-	// stepFive removes the Wireguard link.
-	stepFive
-	// stepSix closes the Wireguard device.
-	stepSix
-	// stepSeven closes the bind connection and the TUN device file.
-	stepSeven
-)