Add CalDav calender without login

### Problem

I wanted to add a public CalDav calender which doesn't need login, but I can't click the "Log In" button in Online Accounts or "Create Calendar" in the Calendar app without entering a username, which then prompts for login.

### Proposal

When creating a new calender from CalDav in Calender, there should be a checkbox to authenticate or not, or a drop down to chose "username/password" or "no auth".

### Prior Art (Optional)

_No response_