chore(lint): add musttag linter and fix lint errors

Breaking change: JSON fields changed in the server API

internal/configuration/settings/portforward.go

@@ -14,12 +14,12 @@ import (
 type PortForwarding struct {
 	// Enabled is true if port forwarding should be activated.
 	// It cannot be nil for the internal state.
-	Enabled *bool
+	Enabled *bool `json:"enabled"`
 	// Filepath is the port forwarding status file path
 	// to use. It can be the empty string to indicate not
 	// to write to a file. It cannot be nil for the
 	// internal state
-	Filepath *string
+	Filepath *string `json:"status_file_path"`
 }
 
 func (p PortForwarding) validate(vpnProvider string) (err error) {