Rename NB_API_ALLOWED_ORIGINS to NB_NAPI_ALLOWED_ORIGINS

[alyssadai]

NB_NAPI_ALLOWED_ORIGINS is the name of the configuration variable in our deployment recipe, which maps to NB_API_ALLOWED_ORIGINS for the API when it is deployed as a Docker container.

To avoid confusion for ourselves and users, we should use the same name for both the environment variable as expected by the API itself, and the environment variable we expect the user to change in their recipe.

Note: neurobagel/recipes will also need to be updated