Adding a 2-phase docker build for testing.

RE:#1431

docker/.gitignore

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+environment.yml

docker/Dockerfile

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+# syntax=docker/dockerfile:1
+
+# Build the InVEST wheel in a separate container stage
+FROM debian:12.2 as build
+RUN apt update && apt install python3 python3-dev python3-pip python3-build build-essential
+RUN python3 -m build && pwd
+
+# Create the container for distribution that has runtime dependencies.
+FROM mambaorg/micromamba:1.5.0-bookworm-slim
+COPY --from build /dist/*.whl /tmp/
+
+# The environment.yml file will be built during github actions.
+COPY --chown=$MAMBA_USER:$MAMBA_USER environment.yml /tmp/environment.yml
+RUN micromamba install -y -n base -c conda-forge -f /tmp/environment.yml && \
+        micromamba clean --all --yes && \
+        /opt/conda/bin/python -m pip install /tmp/*.whl
+
+ENTRYPOINT ["/usr/local/bin/_entrypoint.sh"]
+