By default, Cilium agents read the boot ID from
/proc/sys/kernel/random/boot_id, which is shared among containers
running on the same host. This commit introduces a hidden flag for
specifying the boot ID filename. With this flag set to a different
location, containerized Cilium agents can avoid sharing the same boot
ID.

The previous implementation read /proc/sys/kernel/random/boot_id during
init(), which is no longer feasible because we now need to wait until
the daemon processes the flags. To address this, an initLocalBootID()
function has been introduced to replace init(). Additionally, a new
file, bootid_other.go, has been created to handle non-Linux systems.

Signed-off-by: gray <gray.liang@isovalent.com>

/var/run/cilium/ is mounted to cilium-agent pod via hostPath:

  volumeMounts:
  - mountPath: /var/run/cilium
    name: cilium-run
  volumes:
  - hostPath:
      path: /var/run/cilium
      type: DirectoryOrCreate
    name: cilium-run

By configuring /var/run/cilium/boot_id with a random uuid in Kind
containers, Cilium agents installed with the hidden flag
`boot-id-file=/var/run/cilium/boot_id` will use different boot IDs.

This fixes the CI issue that Cilium agents running locally in Kind
always shared the same boot ID.

Signed-off-by: gray <gray.liang@isovalent.com>