Implement JWT authentication

We want backend to be able to generate and decode JWT from authentication header.

We can use PyJWT package

Implementation expectations:

• Add a api/v2/generate-token route. It will be called as callback_url during oauth user authentication. It should build a token with this payload pattern:

{
  user_id: int,
  deprecatedAt: string
}

• Add a validate_token decorator. It will decode a provided jwt and check if not deprecated.