Support $relativeDir as executorMap parameter

My project is running inside a docker container, and I'd like to create a custom execute command to run the file inside the container. However as there is no parameter for relative path I'm unable to build a command that would be able to locate the file inside the container.

The closest I can get is this:
```bash
docker-compose exec -T my-container bash -c 'php -f $fullFileName'
```

But that doesn't work since the path to the file is completely different inside the container.

**Solution**
Relative path parameter:

```bash
docker-compose exec -T my-container bash -c 'php -f /container/path/to/project/$relativeDir/$fileName'
```