Remove the required field from the schema for ruletypes that can automatically guess the default branch for a repo.

[rdimitrov]

No description provided.

[JAORMX]

This is a good idea. Let's make sure that the upgrade works with minder ruletype apply

[peppescg]

let me add the slack thread for better context

[ethomson]

I didn't do an apply over an existing configuration, but I did do an apply from an empty setup.

[rdimitrov]

@ethomson - I'll give it a test before we close this 👍