feat(docker): add configurable path for vecna.json

* set default config path to /config
* update docker-compose example for config usage
* modify config resolution to include /config directory

Dockerfile

@@ -16,6 +16,10 @@ RUN apk add --no-cache ca-certificates
 
 COPY --from=builder /vecna /usr/local/bin/vecna
 
+ENV VECNA_CONFIG=/config/vecna.json
+
+VOLUME ["/config"]
+
 EXPOSE 8080
 
 ENTRYPOINT ["vecna"]