fix(drone): use full commit SHA for Docker tag and fix non-interactive adduser

- Replace bash substring syntax ${DRONE_COMMIT_SHA:0:7} with
  ${DRONE_COMMIT_SHA} which is supported by Drone YAML variables
- Use 'adduser -D -g ""' in Dockerfile to skip interactive prompts
  for user information during Docker image build

Dockerfile

@@ -23,7 +23,7 @@ FROM eclipse-temurin:21-jre
 WORKDIR /app
 COPY --from=builder /app/build/libs/backend-0.0.1-SNAPSHOT.jar app.jar
 
-RUN adduser --disabled-password --no-create-home appuser && \
+RUN adduser -D -g "" appuser && \
     chown appuser:appuser /app
 USER appuser