Add a docker-compose.yml to run the tests without installing deno

The tests can be run using `docker compose up`. This runs through the tests once. If all tests succeed (as is the case at the time of this commit), the command exits with code `0`. Otherwise, with a non-zero exit code.

Refs:
TELESTION-451 Add Gherkin-based executable specifications for Backend Services

backend-deno/docker-compose.yml

@@ -0,0 +1,7 @@
+services:
+  backend-deno:
+    image: denoland/deno:1.39.0
+    command: ["test", "--allow-all", "/app/cucumber/test.ts"]
+    volumes:
+      - .:/app
+      - ../backend-features:/features