2.4.0 ARM updates

Centos7 deprecation: Kea 2.4.0 ARM CentOS — 7 is still mentioned as one of the Regularly tested Platforms.
https://kea.readthedocs.io/en/kea-2.4.0/arm/quickstart.html#quick-start-guide-using-native-packages update to 2.4.0
hammer.py supported-systems

Edited Jul 13, 2023 by Peter Davies

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information