Get the branching model config for a project

Return the branching model configuration for a project. The returned object: 1. Always has a `development` property for the development branch. 2. Always a `production` property for the production branch. The production branch can be disabled. 3. The `branch_types` contains all the branch types. This is the raw configuration for the branching model. A client wishing to see the branching model with its actual current branches may find the [active model API](#api-workspaces-workspace-proj...