Make the configuration object serve configuration outside the API

[ocelotl]

The configuration object only cares now for OPENTELEMETRY_PYTHON_TRACER_PROVIDER and OPENTELEMETRY_PYTHON_METER_PROVIDER. Nevertheless, some software components that integrate with this project (like the ones in the ext folder or their corresponding auto instrumentation components) may also need to access configuration.

One simple way to do this is to make the configuration object look for any OPENTELEMETRY_PYTHON-prefixed environment variable and add its suffix as an attribute. I am not implementing this right now because more needs may show up soon since more development is being done in auto instrumentation right now.