docs(storage): add comprehensive JSDoc documentation to GetSignedUrlConfig interface properties

[thiyaguk09]

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Fixes #7352

[gemini-code-assist]

Code Review

This pull request adds detailed JSDoc documentation to the properties of the GetSignedUrlConfig interface in handwritten/storage/src/file.ts. The review feedback recommends clarifying the documentation in two areas: first, by explicitly noting that promptSaveAs takes precedence over and overrides responseDisposition if both are provided; and second, by correcting the description of queryParams to specify that only query parameters starting with x-goog- are included in the signature for V4 signed URLs.