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/internal/routemanager/iptables_linux_test.go

@@ -16,11 +16,12 @@ func TestIptablesManager_RestoreOrCreateContainers(t *testing.T) {
 		t.SkipNow()
 	}
 
-	manager, _ := newIptablesManager(context.TODO())
+	manager, err := newIptablesManager(context.TODO(), true)
+	require.NoError(t, err, "should return a valid iptables manager")
 
 	defer manager.CleanRoutingRules()
 
-	err := manager.RestoreOrCreateContainers()
+	err = manager.RestoreOrCreateContainers()
 	require.NoError(t, err, "shouldn't return error")
 
 	require.Len(t, manager.rules, 2, "should have created maps for ipv4 and ipv6")