fix: make grin dir persistent with volume to keep config

Author: ardocrat

Dockerfile

@@ -29,6 +29,8 @@ RUN grin --testnet server config
 RUN sed -i '/^run_tui /s/=.*$/= false/' grin-server.toml
 RUN sed -i '/^api_http_addr /s/=.*$/= "0.0.0.0:13413"/' grin-server.toml
 
+VOLUME ["/root/.grin"]
+
 # Mainnet ports
 EXPOSE 3413 3414