Add default firewall rule to allow netbird traffic (#1056)

Add a default firewall rule to allow netbird traffic to be handled 
by the access control managers.

Userspace manager behavior:
- When running on Windows, a default rule is add on Windows firewall
- For Linux, we are using one of the Kernel managers to add a single rule
- This PR doesn't handle macOS

Kernel manager behavior:
- For NFtables, if there is a filter table, an INPUT rule is added
- Iptables follows the previous flow if running on kernel mode. If running 
on userspace mode, it adds a single rule for INPUT and OUTPUT chains

A new checkerFW package has been introduced to consolidate checks across
route and access control managers.
It supports a new environment variable to skip nftables and allow iptables tests

client/firewall/iptables/manager_linux_test.go

@@ -33,6 +33,8 @@ func (i *iFaceMock) Address() iface.WGAddress {
 	panic("AddressFunc is not set")
 }
 
+func (i *iFaceMock) IsUserspaceBind() bool { return false }
+
 func TestIptablesManager(t *testing.T) {
 	ipv4Client, err := iptables.NewWithProtocol(iptables.ProtocolIPv4)
 	require.NoError(t, err)
@@ -53,7 +55,7 @@ func TestIptablesManager(t *testing.T) {
 	}
 
 	// just check on the local interface
-	manager, err := Create(mock)
+	manager, err := Create(mock, true)
 	require.NoError(t, err)
 
 	time.Sleep(time.Second)
@@ -141,7 +143,7 @@ func TestIptablesManagerIPSet(t *testing.T) {
 	}
 
 	// just check on the local interface
-	manager, err := Create(mock)
+	manager, err := Create(mock, true)
 	require.NoError(t, err)
 
 	time.Sleep(time.Second)
@@ -229,7 +231,7 @@ func TestIptablesCreatePerformance(t *testing.T) {
 	for _, testMax := range []int{10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000} {
 		t.Run(fmt.Sprintf("Testing %d rules", testMax), func(t *testing.T) {
 			// just check on the local interface
-			manager, err := Create(mock)
+			manager, err := Create(mock, true)
 			require.NoError(t, err)
 			time.Sleep(time.Second)