synth: command not found

I am trying to run these benchmarks in a Github Codespace and probably missing something. What is `synth`?

```
/workspaces/imdbench (master ✗) $ make new-dataset
mkdir -p dataset/movies
cat dataset/templates/user.json \
| sed "s/%USERS%/100000/" > dataset/movies/user.json
cat dataset/templates/person.json \
| sed "s/%PEOPLE%/100000/" \
| sed "s/%STARTAT%/6000/" > dataset/movies/person.json
cat dataset/templates/director.json \
| sed "s/%DIRECTORS%/7000/" > dataset/movies/director.json
cat dataset/templates/movie.json \
| sed "s/%MOVIES%/25000/" > dataset/movies/movie.json
cat dataset/templates/review.json \
| sed "s/%REVIEWS%/500000/" \
| sed "s/%MOVIES%/25000/" > dataset/movies/review.json
synth generate dataset/movies > /workspaces/imdbench/dataset/build/protodataset.json
PYTHONPATH=/workspaces/imdbench/ python dataset/cleandata.py
/bin/bash: line 13: synth: command not found
make: *** [Makefile:43: new-dataset] Error 127
```