add backup configuration document

[vankichi]

Description:

SSIA

Related Issue:

How Has This Been Tested?:

Environment:

• Go Version: 1.18.3
• Docker Version: 20.10.8
• Kubernetes Version: 1.22.0
• NGT Version: 1.14.7

Types of changes:

• [ ] Bug fix [type/bug]
• [ ] New feature [type/feature]
• [ ] Add tests [type/test]
• [ ] Security related changes [type/security]
• [x] Add documents [type/documentation]
• [ ] Refactoring [type/refactoring]
• [ ] Update dependencies [type/dependency]
• [ ] Update benchmarks and performances [type/bench]
• [ ] Update CI [type/ci]

Changes to Core Features:

• [ ] Have you added an explanation of what your changes do and why you'd like us to include them?
• [ ] Have you written new tests for your core changes, as applicable?
• [ ] Have you successfully ran tests with your changes locally?

Checklist:

• [ ] I have read the CONTRIBUTING document.
• [ ] I have checked open Pull Requests for the similar feature or fixes?
• [ ] I have added tests and benchmarks to cover my changes.
• [ ] I have ensured all new and existing tests passed.
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have updated the documentation accordingly.

[vdaas-ci]

[CHATOPS:HELP] ChatOps commands.

• :ok_woman: /approve - approve
• :love_letter: /changelog - replace the PR body by changelog details
• :bento: /format - format codes and add licenses
• :white_check_mark: /gen-test - generate test codes
• :label: /label - add labels
• :rewind: /rebase - rebase master
• :end: :two: :end: /label actions/e2e-deploy - run E2E deploy & integration test

[cloudflare-workers-and-pages[bot]]

Deploying with    Cloudflare Pages

Latest commit:	4f121bf
Status:	⚡️  Build in progress...

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[kpango]

It would be better to add 4 points.

1. S3, PV, PV+S3 Use Cases and Merit Demerits
2. Enabling/disabling init-container and its behavior in the case of S3
3. Advantages and disadvantages of CoW enable/disable
4. Concept of each setting item for backup?