feat: add caldav tokens (#1065)

# Description

This PR adds API routes to create and manage caldav tokens. These tokens can be used instead of a user password - required for users who are using external auth providers and don't have a password.

Fixes #842

Frontend: https://kolaente.dev/vikunja/frontend/pulls/1186

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/1065

pkg/user/update_email.go

@@ -63,7 +63,7 @@ func UpdateEmail(s *xorm.Session, update *EmailUpdate) (err error) {
 	}
 
 	update.User.Status = StatusEmailConfirmationRequired
-	token, err := generateNewToken(s, update.User, TokenEmailConfirm)
+	token, err := generateToken(s, update.User, TokenEmailConfirm)
 	if err != nil {
 		return
 	}