fix: rename image_pull_secrets to ImagePullSecrets

[KCSesh]

Issue number:
#708

Description of changes:
Fixed a bug by changing image_pull_secrets to ImagePullSecrets

Testing done:

Setup cross account brupop where IAM role has no access, and use secret to deploy container:

 kubectl create secret docker-registry brupop \
  --docker-server=<cross-account>.dkr.ecr.us-west-2.amazonaws.com \
  --docker-username=AWS \
  --docker-password="${ECR_CROSS_ACCOUNT_PASSWORD}" \
  --namespace=brupop-bottlerocket-aws

kubectl edit deployment brupop-controller-deployment -n brupop-bottlerocket-aws

.
..
...
        image: <cross-account>.dkr.ecr.us-west-2.amazonaws.com/brupop:v1.4.0
        imagePullPolicy: IfNotPresent
        name: brupop
        resources:
          limits:
            memory: 256Mi
          requests:
            cpu: 10m
            memory: 40Mi
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
      dnsPolicy: ClusterFirst
      imagePullSecrets:
      - name: brupop
      priorityClassName: brupop-controller-high-priority
...
..
.

Successful brupop execution done manually:

Every 2.0s: kubectl get bottlerocketshadows --namespace brupop-bottlerocket-aws                                                                                   

NAME                                              STATE                      VERSION   TARGET STATE         TARGET VERSION   CRASH COUNT
brs-ip-<>.us-west-2.compute.internal    Idle                       1.32.0    Idle                                  0
brs-ip-<>.us-west-2.compute.internal   Idle                       1.20.2    Idle                 <no value>       0
brs-ip<>.us-west-2.compute.internal   StagedAndPerformedUpdate   1.20.2    RebootedIntoUpdate   1.32.0           0

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.