Docker image: put /opt/conda/bin on the PATH

Not sure why this is, but when parsl submits a job, it submits the command with
"bash -c <command>" and `/opt/conda/bin` is not on the path, so <command>, which
is provided by conda-installed deps, is not found.

This works with docker, however:

```
docker run ghcr.io/qgreenland-net/parsl-exploration bash -c "<command>"
```

Dockerfile

@@ -9,4 +9,4 @@ COPY --chown=$MAMBA_USER:$MAMBA_USER . .
 RUN micromamba install --yes --name "base" --file "environment.yml"
 RUN micromamba clean --all --yes
 
-# ENV PATH "/opt/conda/bin:${PATH}"
+ENV PATH "/opt/conda/bin:${PATH}"