[FR] Architecture improvements

[Elise17]

This issue is about the future improvements to be made on the architecture.

• Raise the permissions checks present in the layer business to graphql, to avoid it being executed twice in layer rest.
• Create architecture.md at the root level and start to give import that we can execute by layer :
  - blueprints : conversion from the public API to business objects (REST, GraphQL, flask templates)
  - business : work in memory with business objects (should not have adhesion with app.model, should not have adhesion with db from app )
  - datamgmt : persistence, adhesion with the database
• Add a new rule in coding style sheet : "Function names should be prefixed by the module name they belong to, example: iocs_create_instead of create" and apply the rule in the business layer

[c8y3]

I believe the business layer should be able to import from app.models (if only to type the methods arguments). The business layer should not concern itself with persistence details, but still manipulates business objects which are described in app.models.

[c8y3]

An alternative to moving up permissions checks from the business layer into the blueprint layer, would be to have them only in the business layer (that is remove checks that are performed in the REST endpoints annotations)
If graphQL is there to stay, then that would probably be a preferable alternative, since otherwise we are coding the same checks, but in different ways (annotations for the REST endpoints and calls for the graphQL queries)

[c8y3]

We should add issues to clean up the forbidden imports described in the architecture.md file and currently in violation.

[c8y3]

Should from app.schema.marshables imports be forbidden from the persistence layer (datamgmt)?

[c8y3]

We should really rename app.datamgmt into app.persistence: it clearer.

[c8y3]

Moving up permissions_check_current_user_has_some_case_access_stricter ended up into into endpoints /case/report/generate-activities/int:report_id and /case/report/generate-investigation/int:report_id. Shouldn't these endpoints rather be annotated with @ac_api_case_requires(CaseAccessLevel.read_only, CaseAccessLevel.full_access)?

[c8y3]

Should permissions and PermissionDeniedError be moved up into the blueprint namespace?