Add a new custom permission action `render_config` for rendering device and
virtual machine configurations via the REST API. This allows users to render
configurations without requiring the `add` permission.
Changes:
- Add permission check to RenderConfigMixin.render_config() for devices and VMs
- Update API tests to use render_config permission instead of add
- Add tests verifying permission enforcement (403 without render_config)
- Document new permission requirement in configuration-rendering.md
Note: Currently requires both render_config AND add permissions due to the
automatic POST='add' filter in BaseViewSet.initial(). Removing the add
requirement will be addressed in a follow-up commit.
* WIP
* Add config_template field to Device
* Pre-fetch referenced templates
* Correct up_to_date callable
* Add config_template FK to Device
* Update & merge migrations
* Add config_template FK to Platform
* Add tagging support for ConfigTemplate
* Catch exceptions when rendering device templates in UI
* Refactor ConfigTemplate.render()
* Add support for returning plain text content
* Add ConfigTemplate model documentation
* Add feature documentation for config rendering
