v3.0

Lots of new features, and bug fixes.

Features:

• Remove cluster configuration from the stackinator repo so that clusters can be managed separately (#99)
• Support for environment views (#101)
• Simplified build cache configuration (#102)
• Support for CPE 23.03 and cray-mpich 8.1.25 on Alps (#105)
• Created complete online documentation (#107)
  • https://eth-cscs.github.io/stackinator/
• Add a very useful debug script for live-debugging partially built environments (#114)
• Integration of changes from the develop branch of Spack (#122)
• Support for post-install and pre-install hooks (#131) and (#135)
• Support pushing partially built.