feat(inferenceservice): added integration tests to inferenceservice reconcile function

[Al-Pragliola]

Description

This pull request introduces integration tests for the new inferenceservice reconcile feature, and I chose to use envtest to test the functionality, as it is the de facto standard for testing controller-like behavior. Since envtest is not a real Kubernetes cluster, I had to mock responses from the model registry, as you can see in the suite_test.go file, and check that the inference-service-id label is added to the kserve inferenceservice CR. I also found some bugs in the reconciler thanks to the tests, and fixed them in this PR.

NOTE: The large chunk of code in this PR comes from the CRD that needs to be added to the envtest cluster to make it handle inference services.

How Has This Been Tested?

make test

Merge criteria:

• All the commits have been signed-off (To pass the DCO check)

• The commits have meaningful messages; the author will squash them after approval or in case of manual merges will ask to merge with squash.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work.
• Code changes follow the kubeflow contribution guidelines.

[google-oss-prow]

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