api for post upload

[krmax44]

notable changes:

• split up foirequest/api_views.py into multiple files. this is a breaking change i.e. for froide-campaign and froide-food
• add create/update methods to message endpoint
• modified CreateOnlyWithScopePermission, so that regular authentication can also be used. please review carefully, see 3f093af018e1fe720871e7e910ccad96c6adde56

ts client example:

import { retrieveFoiMessage } from './api/index.ts'

retrieveFoiMessage({
  path: { id: '22699' }
}).then((response) => {
  console.log(response.data?.kind) // "email" | "post" | "fax" | "upload" | "phone" | "visit" | "import" | undefined
})