(Docker) Fix passing of POETRY_CACHE_DIR into RUN command (#3163)

* Fix RUN command to get correct value of POETRY_CACHE_DIR

* Fix passing of POETRY_CACHE_DIR into RUN command

* remove test copy of Dockerfile

containers/app/Dockerfile

@@ -26,7 +26,7 @@ RUN apt-get update -y \
 
 COPY ./pyproject.toml ./poetry.lock ./
 RUN touch README.md
-RUN poetry install --without evaluation --no-root && rm -rf $POETRY_CACHE_DIR
+RUN export POETRY_CACHE_DIR && poetry install --without evaluation --no-root && rm -rf $POETRY_CACHE_DIR
 
 FROM python:3.12.3-slim AS runtime