add samples for using a regional endpoint with SCC v2 API

[onagbonoga]

Description

The SCC API can be accessed via Regional Endpoints to meet customer data residency requirements. This sample shows how to override the endpoint for an API client. See https://cloud.google.com/security-command-center/docs/data-residency-support.md#regional-urls for more information on data residency

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• README is updated to include all relevant information
• Tests pass: nox -s py-3.9 (see Test Environment Setup)
• Lint pass: nox -s lint (see Test Environment Setup)
• 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 1 region tag.

• securitycenter/snippets_v2/regional_endpoint_snippet.py:17, tag securitycenter_regional_endpoint_list_findings

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