Add missing poetry export plugin

Dockerfile

@@ -1,9 +1,10 @@
-FROM python:3.9 as builder
+FROM python:3.9 AS builder
 
 COPY . /project
 WORKDIR /project
 
 RUN pip install poetry
+RUN poetry self add poetry-plugin-export
 RUN poetry export --without-hashes -o requirements.txt -f requirements.txt
 RUN poetry build --format=wheel
 RUN cp dist/* /tmp