feat: regional template operations samples

[BigBlackWolf]

Description

Created basic operations for regional templates

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 3 region tags.

• compute/instance-templates/create-instance-templates/create_regional_template.go:17, tag compute_regional_template_create
• compute/instance-templates/create-instance-templates/delete_regional_template.go:17, tag compute_regional_template_delete
• compute/instance-templates/create-instance-templates/get_regional_template.go:17, tag compute_regional_template_get

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[telpirion]

issue: break these into individual tests methods. We should ideally have one test method for each sample.

[BigBlackWolf]

Fair. I've split the test into smaller chunks as you suggested - one per sample.

[telpirion]

Thank you!