Provide a devcontainer setup for Fauxton

[Stwissel]

Overview

This PR provides a devontainer setup for developing Fauxton. There are
** NO CHANGES TO FAUXTON CODE**

Devcontainer use is strictly optional, so nothing changes when a developer doesn't use it. They provide a consistent configuration with standardized dependency versions.

The devcontainer starts Fauxton development and an auxiliary CouchDB side container.
Optional an IdP container for JWT functionality can be added.

Sample configuration scripts are provided (see readme.md)

• populate_couchdb.sh: create databases _users, _relicator, _global_changes and demo
• populate_keycloak.sh: configure the keycloak server with the realm empire, a client fauxton and the users hariseldon, gaaldormick. Furthermore extract the public key from the JWKS, convert it to PEM and configure JWT authentication in CouchDB including trusting that key

Testing recommendations

Open the project in a supported IdE (e.g. VS-Code) and get prompted to reopen the project in devcontainer.
First time configuration might take a while but finally starts npm run dev

GitHub issue number

Fixes #1486

Related Pull Requests

n/a

Checklist

• Code is written and works correctly;
• Changes are covered by tests; -> No change to Fauxton code has been made
• Documentation reflects the changes;
• Update rebar.config.script with the correct tag once a new Fauxton release is made