fix(longhorn): Reduce excessive resource allowcation

By default longhorn deploys with 12% cpu allocated node, that's quite a
lot and takes up 1/3 of the current cluster's CPU. Given how little of
the requested CPU is actually used, this patch reduces the CPU
allocation from 12% to 2%.

IMPORTANT: You should not apply this patch while any of your volumes are
still attached. Therefore scale down all deployments that use volumes,
update the setting, then scale up again.

References:
https://longhorn.io/docs/1.2.3/references/settings/#guaranteed-engine-manager-cpu
https://longhorn.io/docs/1.2.3/references/settings/#guaranteed-replica-manager-cpu