build(agent): add agent init image to related images

[ebaron]

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Fixes: #970
Depends on: #1041

Description of the change:

• This was a piece missed in feat(agent): add pod mutation webhook to inject agent #991 that adds the configurable agent init image to the list of related images in the CSV.

Motivation for the change:

• Needed for disconnected installation of the operator

How to manually test:

1. Build/deploy
2. CSV should have the expected relatedImages entry and corresponding environment variable in the deployment