Safe-settings reapplies collaborator maintain permissions

## Problem Description

The collaborator plugin reads the current permissions from the dict of booleans `permissions` and regenerates the `permission` string from it. But [this logic](https://github.com/github/safe-settings/blob/main-enterprise/lib/plugins/collaborators.js#L28) only support 3 of the 5 built-in roles.

### What is actually happening

This leads to safe-settings performing unnecessary updates when it processes repositories with collaborators that have the `maintain` role, for instance.

### What is the expected behavior

All 5 built-in roles should be supported so that safe-setting only performs updates of collaboration permissions when necessary.

If it is exposed to the application, it would be preferable to read the permission field returned by GitHub directly. This would support all roles, including custom ones.