Update Swagger documentation for REST Api methods

[lraubuch]

Feature Description

When checking the REST Api documentation I came across the method to add a collaborator to a repository.
In the documentation it said, that the payload body needs to contain a permission value which was expected. Unfortunately there was no documentation of what that string value should be to set the appropriate permissions.
After digging deep into the code I found that the permission can be one of three values.

IMHO this should be documented in the Swagger documentation of the REST Api.

Screenshots

[wolfogre]

It's just missed. I don't think it's difficult to add it.