[improve][test] Azure Data Explorer E2E test is always skipped in CI — add a runnable integration test

## Current state

`azure-data-explorer` has `ADXSinkE2ETest`, but it throws `SkipException` unless live Azure credentials (`kustoCluster`, `kustoDatabase`, `kustoAadAppId`, ...) are present in the environment — so CI never exercises the sink. Effective integration coverage is zero.

## Proposal

Use the Microsoft **Kusto emulator** container image (`mcr.microsoft.com/azuredataexplorer/kustainer-linux`) via Testcontainers so the sink can be exercised hermetically in CI, keeping the credential-gated E2E test for live-cluster verification.

_Part of an integration-test coverage sweep of all connector modules._

Start by inspecting the azure-data-explorer ADXSinkE2ETest and its SkipException credential gate, then review how the Kusto emulator image can be started through Testcontainers. Done means CI exercises the sink hermetically without live Azure credentials while the existing credential-gated test remains available for live-cluster verification.

Written by the indexing model from the issue text.