Wrap volumes key in conditional to protect from being nil

[gaffneyd4]

Description of changes:

If webhookTemplateConfigMapName and webhookTemplateConfigMapKey are not set in the values.yaml file, we end up with a deployment.yaml file that has key volumes with a nil value. This causes other tools like kustomize to throw warnings:

2022/01/03 18:04:29 nil value at `volumes.configMap.name` ignored in mutation attempt
2022/01/03 18:04:29 nil value at `volumes.projected.sources.configMap.name` ignored in mutation attempt
2022/01/03 18:04:29 nil value at `volumes.secret.secretName` ignored in mutation attempt
2022/01/03 18:04:29 nil value at `volumes.projected.sources.secret.name` ignored in mutation attempt
2022/01/03 18:04:29 nil value at `volumes.persistentVolumeClaim.claimName` ignored in mutation attempt

This PR wraps the volumes key in the conditional as well so that if it is not being used it doesn't cause these warnings.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[bwagner5]

Awesome! Thank you!