[Tech] Create an API for saving Howtos

[mariojsnunes]

Is your feature request related to a problem? Please describe.
Move our current how-to save to an API using Remix routing.
Should be done by creating two action routes:

• api.howtos.ts for submitting
• api.howtos.$slug.ts for editing

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