deps(ai-platform): update dependencies across ai-platform samples

[angelcaamal]

Description

Fixes b/565434524

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• Required CI tests pass (see CI testing)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

Note: Any check with (dev), (experimental), or (legacy) can be ignored and should not block your PR from merging (see CI testing).

[gemini-code-assist]

Code Review

This pull request updates the Node.js engine requirement to >=20.0.0 and upgrades several dependencies and devDependencies in package.json, including @google-cloud/aiplatform, @google-cloud/bigquery, @google-cloud/storage, c8, and chai. The review feedback correctly points out that upgrading chai to ^6.0.0 will break tests because Chai v5 and above are ESM-only, which is incompatible with this project since it does not specify "type": "module" and likely uses CommonJS. It is recommended to keep chai at ^4.5.0.