Environment updates

[jo-basevi]

This PR grabbed a couple changes from #19, namely:

• Add ENV_LAUNCHER_SCRIPT_PATH to launcher_conf.sh: This means for scripts that are run as part of launcher.sh and within the singularity container, it is possible to find out how to launch the container again. This is useful for payu, so it can pass the launcher script along to the PBS jobs. So the payu pbs jobs would look like: qsub <qsub-flags> -- /path/to/launcher.sh /path/to/squashfs-payu-env/bin/python /path/to/squashfs-payu-env/bin/payu-run. This removes the hack of modifying the payu python headers to point to the python launcher script.
• Update payu/dev to remove modifying payu python header to point to the python launcher script
• Remove CONDA_EXE and MAMBA_ROOT_PREFIX from modulefile as it's not needed as it can cause issues with running payu alongside other conda environments.

Other change:

• Keep 5 latest versions of payu/dev - this is ensure that by the payu/dev environment is deleted, it would be unlikely it was being used in any currently running payu jobs Added in Keep 5 latest versions of payu/dev #21

[aidanheerdegen]

LGTM AFAICT

[jo-basevi]

I've added changes to install netcdf4 with no mpi and removed setting OMPI_MCA_orte_launch_agent to this PR as it's modifying the same files (see #25 for more information). This means mpi and mpich packages will not be installed in the environment.

[aidanheerdegen]

LGTM. Thanks.