reimage backend-hel

[aagbsn]

• make raid1 volume one large root filesystem (remove /dev/md3 for /home and grow fs)
• back up home directories from backend-hel
• upgrade backend-hel to debian stable (trixie)

[aagbsn]

the volume is actually raid1 because backend-hel has 2 disks

[aagbsn]

#452 removes 1 ansible-galaxy dependency from deploy-bootstrap.yml

[aagbsn]

home directories were backed up and a copy placed on clickhouse2

[aagbsn]

Removed the sub-issue #456 as this is a related but larger task