Split NODE_ENV to add an APP_ENV env var

[nfroidure]

Issue

Actually,there is a confusion in the meaning of NODE_ENV that, in fact, have only 3 official values (test, development, production). It is, in fact, supposed to cover more or less what the DEV_MODE=1 env var actually does at the moment (see https://koistya.medium.com/demystifying-node-env-var-b25ed43c9af).

We should create a distinct APP_ENV variable that accept deployments environments like uat, staging ... and load the configurations from it instead of from the NODE_ENV value.

Simply use : https://github.com/nfroidure/application-services/tree/main/src/services