Soothe the CI's ire (#1550)

* Add a bench.Dockerfile
* Add a bench target to the makefile

Author: voodoos

Makefile

@@ -18,4 +18,6 @@ preprocess:
 promote:
 	dune promote
 
-.PHONY: all build dev clean test promote
+bench:
+
+.PHONY: all build dev clean test promote bench

bench.Dockerfile

@@ -0,0 +1,9 @@
+FROM ocaml/opam:ubuntu-20.04-ocaml-4.14
+
+WORKDIR /app
+
+RUN sudo apt-get update
+RUN sudo apt-get -y install jq
+COPY . .
+RUN sudo chown -R opam /app
+RUN eval $(opam env)