core: frontend: allow fetching/extracting "permissions" for manually installed Extensions

### Current behaviour

Extensions installed through the store have access to the developer's recommended `permissions` / Docker container settings, because they're included in the store manifest. Manually installed Extensions don't have a manifest, so settings need to be entered manually, because we don't get them until the Extension has already been installed.

Not having access to those pre-defined settings is annoying[^1], and can be confusing (because it may seem like there are no intended settings, but then the installed Extension doesn't work properly). Being able to directly use the pre-defined settings could also help identify issues with them early, before the Extension ends up on the store.

[^1]: especially because they're specified in the Dockerfile as backslash-escaped text, which then needs every line manually edited unless they're also maintained in the README or similar for easy copy-pasting

### Expected or desired behaviour

1. We should at least make it clearer in the manual installation interface that "original settings" can be found in the Dockerfile
2. If the user has not specified settings, we should try to automatically extract them from the `permissions` label of the downloaded Docker image, before we try to run it as a container
3. Ideally we would allow users to pre-fetch the settings somehow, within the "create" dialog, before they finish registering the Extension
- If need be this could be a button that downloads the specified Docker image and extracts the data from the label, and then confirming out of the creation dialog could just register and run the already downloaded image

### Additional context
- I seem to recall this having been discussed internally a while ago, as an annoyance, but without a presented solution
- It has also now been [asked about in a forum post](https://discuss.bluerobotics.com/t/automatically-loading-extensions-settings-from-docker-file-permissions-label/22661)

### Prerequisites

- [x] I have checked to make sure that a similar request has not already been filed or fixed.