Add CSP configuration validation to SageMaker build workflow

[feiyangliu2023]

Issue #, if available:
D322618311

Description of changes:

Description

Adds CSP (Content Security Policy) configuration validation to the build workflow for the code-editor-sagemaker-server target.

Changes

• Added CSP validation step in .github/workflows/build-targets.yaml
• Only executes for code-editor-sagemaker-server target

Testing

Remote

Ran build-target github action two times, before and after modifying 'patches/sagemaker/update-csp.diff', which changes CSP text.
Received one success and one failure outcome, as expected.
Link:
https://github.com/feiyangliu2023/code-editorv2/actions/runs/18529763981
https://github.com/feiyangliu2023/code-editorv2/actions/runs/18531210588

Local

Created two test scripts to verify both success and failure scenarios:
Success:

• Applies patches for code-editor-sagemaker-server
• Verifies CSP text exists in patched file
• Test passes - CSP check correctly validates the configuration
  Faiure:
• Applies patches and modifies file to remove CSP text
• Verifies check detects missing CSP configuration
• Test passes - CSP check correctly fails and detects the issue

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