Common microservice: get runtime environment

Nobody has claimed this yet.

Currently there is no generic way to setup configurations that are different on the different environments in the frontend, at runtime. One example is the google analytics tag between dev and prod environment.

The common microservice provides that for Sentry and Accounts but there is no generic way to add more.

A new endpoint can be added to the common microservice to get global configurations, say `GET api/environment?var=A`.

This will return the configuration variable named "A" (note that is better not to expose any environmental variable from the runtime, but only the values that are intended to)

Start by locating the common microservice and its existing Sentry and Accounts configuration endpoints. Trace how runtime configuration is exposed, then determine where the proposed GET api/environment?var=A behavior should be covered. Done means an approved configuration variable can be retrieved for frontend use without exposing arbitrary environment variables.

Written by the indexing model from the issue text.