Instead of using just strings, this change converts the scopes to a
`StrEnum`, to be compatible with places where a string is expected. This
avoids typos when using these scopes, simplifies searching for usages,
and improves type hints.
An extra change was the fix to the Firmware download endpoint, which
wasn't respecting the `DISABLE_DOWNLOAD_ENDPOINT_AUTH` flag.
According to multiple FastAPI discussions [1], FastAPI only includes a
built-in mechanism to redirect requests including a trailing slash, to
its variation without slash, using a `307` status code.
This can be an issue when certain clients do not send the same headers
on the redirected request.
This change adds a custom FastAPI `APIRouter`, that registers both route
path variations (with and without trailing slash), while only marking
the path without slash for being included in the OpenAPI schema.
[1] https://github.com/fastapi/fastapi/discussions/7298
