[Spike] Allow extensions to contribute custom convention for environment-specific operational configuration

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**Timeboxed to 2 weeks**; don't spend extra time if done earlier

Different platforms use different ways for configuring operational aspects of application in test/dev/production. LB4 should make it easy to write extensions to support these different platforms.

The goal of this spike is to find out and document what's possible today, identify gaps, propose solutions and create a list of follow-up tasks.

Few examples of operational config:
- configure datasources from environment variables
- use a faster but less-secure hashing algorithm in dev/test (a hashing algorithm is used e.g. to store user passwords)
- apply datasource configuration provided by `VCAP_SERVICES` env variable in CloudFoundry/IBM Cloud - see https://github.com/strongloop/loopback-next/pull/1574

Possibly related: https://github.com/strongloop/loopback-next/pull/983 and https://github.com/strongloop/loopback-next/issues/1396

Inizia esaminando il supporto attuale per le estensioni di LoopBack 4 e la configurazione operativa, quindi leggi le pull request correlate 1574 e 983 e l’issue 1396. Documenta ciò che è possibile oggi, individua le lacune, proponi soluzioni ed elenca attività concrete di follow-up; il completamento consiste nel risultato documentato dello spike entro il limite di due settimane.

Scritto dal modello di indicizzazione a partire dal testo della issue.