Re-work Swagger UI configuration

It turns out that Swagger UI mostly does the "right" thing for our
use cases here, but it assumes that API paths are relative to the
root of the host where it is being served. This works in the local
development environment because we are serving on "/", but it does
not work in production where the API is deployed beneath the DSpace
REST API, for example at "/rest/statistics".

The solution here is to allow configuration of the DSpace Statistics
API path and use that when registering the Swagger UI as well as in
a new "server" block in the OpenAPI JSON schema.

By default it is configured to work out of the box in a development
environment. Set the DSPACE_STATISTICS_API_URL environment variable
to something like "/rest/statistics" when running in production.

dspace_statistics_api/config.py

@@ -9,12 +9,12 @@ DATABASE_PASS = os.environ.get("DATABASE_PASS", "dspacestatistics")
 DATABASE_HOST = os.environ.get("DATABASE_HOST", "localhost")
 DATABASE_PORT = os.environ.get("DATABASE_PORT", "5432")
 
-# SwaggerUI configuration
-
-# URI path where the Swagger UI should be available (without trailing slash)
-SWAGGERUI_URL = os.environ.get("SWAGGERUI_URL", "/swagger")
-# URI path to the OpenAPI JSON schema
-SWAGGERUI_SCHEMA_URL = os.environ.get("SWAGGERUI_SCHEMA_URL", "/docs/openapi.json")
+# URL to DSpace Statistics API, which will be used as a prefix to API calls in
+# the Swagger UI. An empty string will allow this to work out of the box in a
+# local development environment, but for production it should be set to a value
+# like "/rest/statistics", assuming that the statistics API is deployed next to
+# the vanilla DSpace REST API.
+DSPACE_STATISTICS_API_URL = os.environ.get("DSPACE_STATISTICS_API_URL", "")
 
 VERSION = "1.4.0-dev"