[Enhancement] Run cluster based integration tests as e2e tests & enable them in prow using emulators

[anveshreddy18]

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Enhancement (What you would like to be added):

Currently the integration tests and integrationcluster tests of etcdbr are under test/e2e folder. This issue aims to enable these e2e tests to be run as prow job upon whenever a PR is raised like in etcd-druid. Configure the prow job to be run with storage emulators like localstack, fake-gcs-server & Azurite instead of real infra. And also move the integration tests to under test/ to standardise the directory structure.

The tests can also be configured to run with real infra, this way developers can be sure about their changes especially to the storage SDKs and APIs.

Motivation (Why is this needed?):

By having e2e tests separately, it can be run as a standalone test in prow job with multiple cloud storage emulators running in parallel, as this will ensure any changes made to the codebase are properly tested with different cloud providers before pushing them.

Approach/Hint to the implement solution (optional):