Updates for Rocky, plus updates to allow the script to be run by the custom image generator

• reduce log noise a little
• Only unhold systemd on debian12
• encode get_metadata_value logic inline so this script works where /usr/share/google/get_metadata_value is not installed (custom-images)
• clean up argument passing to execute_with_retries
• allow access to DKMS keys for the duration of the install process instead of just during driver signing
• On Rocky, try to build drivers using DKMS with a fallback of installing pre-built binaries
• Do not install driver aliases on rocky
• remove extra modprobe -r
• in configure_yarn, skip update if ${HADOOP_CONF_DIR} does not exist
• only chown yarn:yarn for directory list if directory list is not empty (including existing as a single element with element value 'None')
• corrected logic to modify the bigtop sources.list file rather than generating a new one
• using $(os_codename) rather than ${OS_CODENAME}
• google cloud + logging/monitoring sources.list section tidy-up
• MySQL key is now fetched from keyserver.ubuntu.com rather than including inline
• making a backup of /etc/apt/trusted.gpg instead of removing without backup
• unholding systemd and libsystemd0 on bookworm instead of force-upgrading