Container-in-a-container issues

Hi all,

Thought I would open up an issue to discuss the container-in-a-container issues that we in UKCEH (@CansuUluseker and @mjhollaway) are having.

Our goal is to use eWaterCycle within a [DataLab project](https://datalab.datalabs.ceh.ac.uk/), but this is generally relevant to any system built on containers.

Suggestions for us to focus on after our latest meeting:
* Try the leaky bucket example, following the [local Python tips here](https://github.com/eWaterCycle/ewatercycle-leakybucket/blob/main/plugin_guide.md#local-python-model). Could also try this related example: https://github.com/Daafip/ewatercycle-hbv
* Investigate whether giving Apptainer `setuid` privileges is an option within DataLabs (which might be more relevant discussed as an issue in [this repo](https://github.com/eWaterCycle/grpc4bmi), if I understood correctly?). This issue might be of relevance: https://github.com/eWaterCycle/grpc4bmi/issues/27

Did I forget anything important or get any of that wrong?