var source = new EnvironmentVariablesSource();
Keys with dots, colons and double underscores are treated as hierarchical and get split into segments:
throttling.capacity=50 --> { "throttling": { "capacity": "50" } }
throttling:capacity=50 --> { "throttling": { "capacity": "50" } }
throttling__capacity=50 --> { "throttling": { "capacity": "50" } }
This source is static and never issues data updates.
