en: add doc about volume snapshot backup/restore across multiple kubernetes

[WangLe1321]

What is changed, added, or deleted? (Required)

Preview:

• deploy-br-federation-manager
• backup-by-ebs-snapshot-across-multiple-kubernetes
• restore-by-ebs-snapshot-across-multiple-kubernetes

Which TiDB Operator version(s) do your changes apply to? (Required)

• [x] master (the latest development version)
• [x] v1.5 (TiDB Operator 1.5 versions)
• [ ] v1.4 (TiDB Operator 1.4 versions)
• [ ] v1.3 (TiDB Operator 1.3 versions)
• [ ] v1.2 (TiDB Operator 1.2 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s):

[CLAassistant]

All committers have signed the CLA.

[lilin90]

I haven't finished my review and is continuing reviewing another two files.

[WangLe1321]

I updated the documentation in 2 commits, please review again @lilin90 @ran-huang

[BornChanger]

I updated the documentation in 2 commits, please review again @lilin90 @ran-huang

I just added 2 commits fcba2c1103098632722be2e81bc8d566b6c0f031 and 0d2026ce906a6aaeea15c43863bd552eb30061a1 in faq, please review as well. @lilin90 @ran-huang

[BornChanger]

Any pending comments or issues now? @WangLe1321 @ran-huang

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2023-09-01 09:48:07.736094179 +0000 UTC m=+2093252.285110165: :ballot_box_with_check: agreed by ran-huang.

[ti-chi-bot[bot]]

@BornChanger: adding LGTM is restricted to approvers and reviewers in OWNERS files.

In response to [this](https://github.com/pingcap/docs-tidb-operator/pull/2406#pullrequestreview-1606634117): > Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[ran-huang]

/approve

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ran-huang

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/pingcap/docs-tidb-operator/blob/master/OWNERS)~~ [ran-huang] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-1.5: #2446.