Support projected volumes as additionalVolumes

[Capitrium]

Description

This allows using a projected volume under spec.general.additionalVolumes.

My specific use case is to allow using a serviceAccountToken mount to enable AWS IAM Roles for service accounts on EKS (and EC2) clusters, though I'm sure there are others.

Issues Resolved

List any issues this PR will resolve, e.g. Closes [...]. Fixes #459

Check List

• [x] Commits are signed per the DCO using --signoff
• [x] Unittest added for the new/changed functionality and all unit tests are successful
• [x] Customer-visible features documented
• [x] No linter warnings (make lint)

If CRDs are changed:

• [x] CRD YAMLs updated (make manifests) and also copied into the helm chart
• [x] Changes to CRDs documented

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[prudhvigodithi]

Thanks @Capitrium and @swoehrl-mw.