serializeImagePulls should be passed in kubelet config file instead of flag

[vinayakk-sahaj]

/kind bug

1. What kops version are you running? The command kops version, will display
this information.
1.28.4 however applies to latest as well

2. What Kubernetes version are you running? kubectl version will print the
version if a cluster is running or provide the Kubernetes version specified as
a kops flag.

1.28.4 however applies to latest as well

3. What cloud provider are you using?
AWS

4. What commands did you run? What is the simplest way to reproduce this issue?
created cluster with below config,

spec:
  kubelet:
     serializeImagePulls: false

5. What happened after the commands executed?
Nodes were added to the cluster, however rolling was slow due image pulling happening in serial.

6. What did you expect to happen?
Parallel image pull at the startup of the node

7. Please provide your cluster manifest. Execute
kops get --name my.example.com -o yaml to display your cluster manifest.
You may want to remove your cluster name and other sensitive information.

spec:
  kubelet:
     serializeImagePulls: false

8. Please run the commands with most verbose logging by adding the -v 10 flag.
Paste the logs into this report, or in a gist and provide the gist link here.

9. Anything else do we need to know?

This document as well as cli says this flag is deprecated

https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet/#:~:text=has%20more%20details.%20(-,DEPRECATED%3A%20This%20parameter%20should%20be%20set%20via%20the%20config%20file%20specified%20by%20the%20kubelet%27s%20%2D%2Dconfig,-flag.%20See%20kubelet

Happy to contribute if this is confirmed issue.