build: devstack ecommerce reaches coordinator on host.docker.internal

settings/base.py currently points COMMERCE_COORDINATOR_SERVICE_URL to
localhost.

But commerce-coordinator isn't in devstack yet.

Because localhost is the local Docker network (and not the host machine)
within a Docker container, ecommerce in devstack won't be able to reach
commerce-coordinator.

host.docker.internal is an internal Docker alias for the host machine
running Docker Desktop. (localhost from within a Docker container is the
container itself, not the machine running Docker Desktop.)

Use host.docker.internal instead of localhost to connect to Coordinator.

ecommerce/settings/devstack.py

@@ -66,6 +66,8 @@
 
 ENTERPRISE_ANALYTICS_API_URL = 'http://edx.devstack.analyticsapi:19001'
 
+COMMERCE_COORDINATOR_SERVICE_URL = 'http://host.docker.internal:8140'
+
 # PAYMENT PROCESSING
 PAYMENT_PROCESSOR_CONFIG = {
     'edx': {