chore: add startup probe to avoid false unhealthy events

[fmuyassarov]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Give the driver enough time to complete plugin registration before throwing unhealthy events, which may give wrong signal. While introducing events in #221, I noticed probe failure events on the driver Pod and I was a bit confused for a while until I realized that readinessProbe was faster than DRANET waiting timeout for the kubelet to complete plugin registration (30 sec). Thus, adding startup timeout should avoid getting false positives even if the registration timeout takes longer but no more than 30 sec which is set here.

I've given in total 60s for the startup probe (2 times 30s timeout set for the kubelet plugin registration) and those extra seconds basically to cover image pulling and other stuff that are not directly about the driver itself.

before

Events:
  Type     Reason     Age   From               Message
  ----     ------     ----  ----               -------
  Normal   Scheduled  14s   default-scheduler  Successfully assigned kube-system/dranet-7sxql to dra-worker2
  Normal   Pulled     13s   kubelet            spec.containers{dranet}: Container image "registry.k8s.io/networking/dranet:v1.3.0" already present on machine and can be accessed by the pod
  Normal   Created    13s   kubelet            spec.containers{dranet}: Container created
  Normal   Started    13s   kubelet            spec.containers{dranet}: Container started
  Warning  Unhealthy  13s   kubelet            spec.containers{dranet}: Readiness probe failed: Get "http://172.18.0.3:9177/healthz": dial tcp 172.18.0.3:9177: connect: connection refused
  Warning  Unhealthy  12s   kubelet            spec.containers{dranet}: Readiness probe failed: HTTP probe failed with statuscode: 503

after

Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  29m   default-scheduler  Successfully assigned kube-system/dranet-m2gwf to dra-worker
  Normal  Pulling    29m   kubelet            spec.containers{dranet}: Pulling image "ttl.sh/dranet:3aa6a69"
  Normal  Pulled     29m   kubelet            spec.containers{dranet}: Successfully pulled image "ttl.sh/dranet:3aa6a69" in 4.939s (4.939s including waiting). Image size: 46028325 bytes.
  Normal  Created    29m   kubelet            spec.containers{dranet}: Container created
  Normal  Started    29m   kubelet            spec.containers{dranet}: Container started

Which issue(s) this PR is related to:

"N/A".

Special notes for your reviewer:

Does this PR introduce a user-facing change?

 "NONE"

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: fmuyassarov
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