Testing: add controller webhooks unit test

[fabriziosestito]

Is your feature request related to a problem?

We want to test the controller's webhooks certificate bootstrap logic. The test should test:

• Given a clean state, when the user installs the controller chart, then the certificates are generated and stored in the secrets, and the CA bundle is injected into the webhooks configuration.
• Given an existing installation, when the user upgrades the controller chart, then the certificates and CA bundles are not changed.

This issue depends on: #507

Solution you'd like

No response

Alternatives you've considered

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Anything else?

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