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

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

まず、現在の LoopBack 4 拡張機能と運用構成のサポートを確認し、続いて関連する pull request 1574 と 983、および issue 1396 を読んでください。現在可能なことを文書化し、不足している点を特定し、解決策を提案し、具体的なフォローアップタスクを一覧にしてください。この作業の完了条件は、2週間の期限内に spike の結果を文書化することです。