feat(routeoptimization): basic request doc snippet

[bshi]

Description

Adds new documentation snippet for Route Optimization API

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)

  I have done this already.

• 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

  I have permission to create groups in the org I can't update CODEOWNERS until it gets permissions for this repo

• 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 1 region tag.

• routeoptimization/snippets/optimize_tours.go:17, tag routeoptimization_optimize_tours

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