Adds mount-cacheing for pip in Dockerfile (#383)

# Description

We frequently reinstall pip packages when building the docker, even when
the downloaded packages have not changed between builds. This allows us
to look in `/root/.cache/pip` (on the image) for cached pip packages.
This speeds up our build significantly.

Adds a [mount cache
](https://docs.docker.com/build/cache/#use-the-dedicated-run-cache)to
the Dockerfile for the line `${ORBIT_PATH}/orbit.sh --install --extra`,
significantly increasing speeds by preventing repeated downloads of
large packages

## Type of change

- New feature (non-breaking change which adds functionality)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have run all the tests with `./orbit.sh --test` and they pass
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

docker/Dockerfile

@@ -65,7 +65,10 @@ RUN touch /bin/nvidia-smi && \
     touch /var/run/nvidia-persistenced/socket
 
 # installing Orbit dependencies
-RUN ${ORBIT_PATH}/orbit.sh --install --extra
+# use pip caching to avoid reinstalling large packages
+RUN --mount=type=cache,target=/${DOCKER_USER_HOME}/.cache/pip \
+    ${ORBIT_PATH}/orbit.sh --install --extra
+
 # aliasing orbit.sh and python for convenience
 RUN echo "alias orbit=${ORBIT_PATH}/orbit.sh" >> ${HOME}/.bashrc && \
     echo "alias python=${ISAACSIM_PATH}/python.sh" >> ${HOME}/.bashrc && \