[node][proposal] Add node to PATH

Currently we need to add "magic", absolute path to node binary in health cmd:
```Dockerfile
# myapp
CMD [ "./server.js" ]
HEALTHCHECK CMD [ "/nodejs/bin/node", "./healthcheck.js" ]
```
If we were to enrich the environment variable PATH it would be unnecessary:

```Dockerfile
# distroless/nodejs
ENV PATH=/nodejs/bin/:$PATH
# myapp
CMD [ "./server.js" ]
HEALTHCHECK CMD [ "node", "./healthcheck.js" ]
```

What do you think about this improvement?