feat(genai sdk): text generation samples with GCS audio and video

[Valeriy-Burlaka]

Description

Adds samples for text generation using the new GenAI SDK — with audio and video inputs located in GCS. Added region tags:

• googlegenaisdk_textgen_with_mute_video
• googlegenaisdk_textgen_with_video
• googlegenaisdk_textgen_with_gcs_audio
• googlegenaisdk_textgen_transcript_with_gcs_audio

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 5 region tags.

• genai/text_generation/textgen_transcript_with_gcs_audio.go:18, tag googlegenaisdk_textgen_transcript_with_gcs_audio
• genai/text_generation/textgen_with_gcs_audio.go:18, tag googlegenaisdk_textgen_with_gcs_audio
• genai/text_generation/textgen_with_mute_video.go:18, tag googlegenaisdk_textgen_with_mute_video
• genai/text_generation/textgen_with_txt.go:18, tag googlegenaisdk_textgen_with_txt
• genai/text_generation/textgen_with_video.go:18, tag googlegenaisdk_textgen_with_video

---

This comment is generated by snippet-bot.
If you find problems with this result, please file an issue at:
https://github.com/googleapis/repo-automation-bots/issues.
To update this comment, add snippet-bot:force-run label or use the checkbox below:

• Refresh this comment

[holtskinner]

This file is already added in #5127

[Valeriy-Burlaka]

Yes, that's expected!