reorganise/cleanup Makefile
Summary
The Makefile has a number of different make targets, but some have unclear meaning or are inconsistent between targets
Bug behavior
For example, the develop-conda target now also updates the conda environment and doesn't work similar to the develop-pep517. We probably should have a very clear and simple set of instructions and build targets, one for "normal" users and one for "developers". Anything else can be optionally included but it should be clear it's not what you normally should be doing. This bug should probably feed into #515
Once this is fixed, we can also (hopefully) clean up the CI/CD script, for which I will open a different issue.