[ci-visibility] Improve `NODE_OPTIONS` instructions

[juan-fernandez]

What does this PR do?

Add instructions to keep value of NODE_OPTIONS when using CI Visibility for javascript.

Motivation

Reduce the likelihood of the user overwriting NODE_OPTIONS.

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• [ ] Review the changed files.
• [ ] Review the URLs listed in the Preview section.
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• [ ] Review any mentions of "Contact Datadog support" for internal support documentation.

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Modified Files

• https://docs-staging.datadoghq.com/juan-fernandez/improve-node-options-docs/continuous_integration/setup_tests/javascript