Refactor the configuration defaults handling code

[shmuelk]

This PR refactors the code that sets the various defaults in the loaded configuration.

In particular this PR:

• Centralizes all of the defaults setting code into one file under pkg/epp/config/loader
• Defaults are no longer set as side affects of instantiating plugins or configuration validation
• The configuration loader now returns an EPP configuration object that does not reference the K8S CRD like configuration objects.

In addition various configurations in the code base have been modified to remove from them default "items".

Fix: #1169

[k8s-ci-robot]

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[nirrozenbaum]

/ok-to-test

[nirrozenbaum]

/cc @ahg-g

[ahg-g]

Great, so here we have the defaulted configuration logged with one exception, the plugins parameters defaults.

[ahg-g]

/lgtm
/approve

Thanks, much better than before. Ideally the plugins parameters defaults are included somehow and logged as well

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahg-g, shmuelk

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