Important

Add GitHub Actions workflow and unit tests for Helm chart with setup instructions in README.

• GitHub Actions:
  • Adds .github/workflows/test.yaml to run Helm unit tests on pull_request and push to main.
  • Uses actions/checkout@v4, azure/setup-helm@v3, and EnricoMi/publish-unit-test-result-action@v2.
  • Installs helm-unittest plugin and runs tests on charts/langfuse/.
• README:
  • Adds testing section with setup and local test running instructions.
• Tests:
  • Adds basic_test.yaml and minimal-installation_test.yaml in charts/langfuse/tests/.
  • basic_test.yaml: Tests rendering with default values, app labels, and image specification.
  • minimal-installation_test.yaml: Tests rendering of basic resources, secret references, and database connections.

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