fix: autogenerated code to allow passthrough schemas to prevent Zod field stripping

[margaretjgu]

closes #155
relates to https://github.com/elastic/elastic-client-generator-js/pull/159

Tested fix:

• did a bulk index and _source was properly propagated compared to empty object before

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no	no	3.19s
✅ REPOSITORY	gitleaks	yes		no	no	8.33s
✅ REPOSITORY	git_diff	yes		no	no	0.04s
✅ REPOSITORY	secretlint	yes		no	no	2.08s
✅ REPOSITORY	trivy	yes		no	no	13.99s
✅ TYPESCRIPT	eslint	3		0	0	2.31s

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