dashboard: reduce noise in current kernel version

dashboard: reduce noise in current kernel version

use the new 'current-kernel' object returned by the node status API to
render a more usable (less noise) version information.

Keep fallback for old one to better work with upgrades (major and
minor) to this version in a cluster, where the web UI one uses might
be the new one, but a node one looks at still have the old API daemon.

Mirrors commit be04f8ee ("ui: node summary: reduce noise in current
kernel version") and commit 4fb7e9e4 ("fix #5121: ui: node status:
avoid invalid array access for certain foreign kernels") from
pve-manager.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>