feat(genai sdk): text generation samples using tools

[Valeriy-Burlaka]

Description

Adds samples for text generation with the new GenAI SDK and tools. Added region tags:

• googlegenaisdk_tools_code_exec_with_txt
• googlegenaisdk_tools_code_exec_with_txt_local_img
• googlegenaisdk_tools_func_desc_with_txt
• googlegenaisdk_tools_google_search_with_txt

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

[snippet-bot]

Here is the summary of changes.

You are about to add 4 region tags.

• genai/tools/code_exec_with_txt.go:18, tag googlegenaisdk_tools_code_exec_with_txt
• genai/tools/code_exec_with_txt_local_img.go:18, tag googlegenaisdk_tools_code_exec_with_txt_local_img
• genai/tools/func_desc_with_txt.go:18, tag googlegenaisdk_tools_func_desc_with_txt
• genai/tools/google_search_with_txt.go:18, tag googlegenaisdk_tools_google_search_with_txt

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[holtskinner]

This is a duplicate, it's already created in #5127

[Valeriy-Burlaka]

@holtskinner , I know! All of these PRs are based on #5127, which will be merged first once #5124 (Go version bump to 1.23) is out. I will clean up things before any subsequent merges.

[Valeriy-Burlaka]

@holtskinner , I cleaned up the diff, — please take another look!