fix: refactoring aiplatform samples

[BigBlackWolf]

Description

• Refactoring samples to put hidden variables inside samle

Checklist

• [ ] I have followed Contributing Guidelines from CONTRIBUTING.MD
• [ ] Tests pass: go test -v ./.. (see Testing)
• [ ] Code formatted: gofmt (see Formatting)
• [ ] Vetting pass: go vet (see Formatting)
• [ ] 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 sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners 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

[BigBlackWolf]

It appears to be two identical samples in embeddings.go and _embeddingspreview.go: generativeaionvertexai_sdk_embedding and generativeaionvertexai_text_embeddings / aiplatform_text_embeddings. Should one of them being removed?

[telpirion]

It appears to be two identical samples in embeddings.go and _embeddingspreview.go: generativeaionvertexai_sdk_embedding and generativeaionvertexai_text_embeddings / aiplatform_text_embeddings. Should one of them being removed?

Yes, If the two samples are identical, we should remove one of them. If I had to guess, one was written when the feature was in a preview state.