Split code into modules

This is a massive commit that restructures the code into modules:

db/
    All functions related to modifying the Database

types/
    All type definitions and methods that can be exclusivly used on
    these types without dependencies

policy/
    All Policy related code, now without dependencies on the Database.

policy/matcher/
    Dedicated code to match machines in a list of FilterRules

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/protocol_common_utils.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"sync"
 
+	"github.com/juanfont/headscale/hscontrol/types"
 	"github.com/juanfont/headscale/hscontrol/util"
 	"github.com/klauspost/compress/zstd"
 	"github.com/rs/zerolog/log"
@@ -15,7 +16,7 @@ import (
 
 func (h *Headscale) getMapResponseData(
 	mapRequest tailcfg.MapRequest,
-	machine *Machine,
+	machine *types.Machine,
 	isNoise bool,
 ) ([]byte, error) {
 	mapResponse, err := h.generateMapResponse(mapRequest, machine)
@@ -43,7 +44,7 @@ func (h *Headscale) getMapResponseData(
 
 func (h *Headscale) getMapKeepAliveResponseData(
 	mapRequest tailcfg.MapRequest,
-	machine *Machine,
+	machine *types.Machine,
 	isNoise bool,
 ) ([]byte, error) {
 	keepAliveResponse := tailcfg.MapResponse{