[Tech] Create API for downloading Howto files

[mariojsnunes]

Is your feature request related to a problem? Please describe.
Have an API to download howto files using Remix routing.
Should be done by creating the route: api.howtos.$id.files.$fileId.ts

The API must increase the download count.
The API must validate the authenticated user.

Additional context
This is part of the effort to decouple the firebase from the client to make it easier for a Supabase migration.
And also improve codebase maintainability.

Blocked by:

1. [Tech] Server-side Auth #3960