Fix e2e tests with storage emulators by using EndpointOverride

[anveshreddy18]

How to categorize this PR?

/area storage
/area testing
/kind test

What this PR does / why we need it:

This PR fixes the e2e tests with storage emulators by using EndpointOverride. The etcdbr PR#1000 removes the deprecation support for passing endpoint override through credentials, but the e2e tests in etcd-druid still use old way of passing it through secrets, this PR now updates that and updates documentation regarding that.

To be more specific, the e2e tests with storage emulators (Localstack, Azurite, FakeGCS) were broken because the test utilities were still generating deprecated secret fields (endpoint, domain, storageAPIEndpoint) that are no longer processed by etcd-backup-restore starting from 0.42.0

This change:

• Updates test utilities to set EndpointOverride in the Etcd CR spec based on emulator environment variables
• Removes deprecated field generation from GenerateBackupSecretData()
• Fixes documentation with correct in-cluster service addresses
• Adds detailed e2e setup instructions for each emulator

Which issue(s) this PR fixes:
Fixes #

Checklist:

• Update documentation in the /docs folder (if applicable)
  • If new files added to docs, or docs structure modified:
    • Update mkdocs.yml. Follow Updating Documentation guide to test the changes locally.
    • Update Table of Contents for the docs.
• Add tests that cover your changes (if applicable)
  • Unit tests
  • Integration tests
  • E2E tests

Special notes for your reviewer:

Release note:

The e2e tests with storage emulators (Localstack, Azurite, FakeGCS) have been fixed w.r.t endpoint override.

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[gardener-prow]

@anveshreddy18: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-etcd-druid-e2e-kind-recovery	046403d	link	true	/test pull-etcd-druid-e2e-kind-recovery

Full PR test history. Your PR dashboard. Command help for this repository.
Please help us cut down on flakes by linking this test failure to an open flake report or filing a new flake report if you can't find an existing one. Also see our testing guideline for how to avoid and hunt flakes.

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