Issue 589: Add imagePullSecrets for Helm hooks

[unguiculus]

Change log description

• Adds imagePullSecrets to the service accounts for the Helm hooks
• Follows the same principle as the service account for the operator taking global imagePullSecrets into account

Purpose of the change

Fixes #589

What the code does

Adds imagePullSecrets to the YAML for the ServiceAccounts for the Helm hooks. This is important when images are pulled from a private registry, e.g. an internal proxy, such as Artifactory, or when using custom images.

How to verify it

Render the templates using the following command:

helm template zookeeper charts/zookeeper-operator \
    --show-only templates/post-install-upgrade-hooks.yaml \
    --show-only templates/pre-delete-hooks.yaml \
    --set hooks.serviceAccount.imagePullSecrets={'my-pull-secret'}

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (9fc6151) 85.91% compared to head (7fa4bdb) 85.91%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #591 +/- ## ======================================= Coverage 85.91% 85.91% ======================================= Files 12 12 Lines 1633 1633 ======================================= Hits 1403 1403 Misses 145 145 Partials 85 85 ```

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[krishnadas-menon]

@jkhalack Would you be able to have a look at this change? It would be really appreciated to get this change added to the helm charts. TIA

[krishnadasm]

@anishakj Could you please help me with the timeline for this change to be released. Appreciate if you could expedite the same. Thanks in advance.

[crazyzhou]

Merged as admin.