Clarify statement on backup-and-restore-using-dumpling page

[dveeden]

What is changed, added or deleted? (Required)

1. The statement to install lightning wasn't correct
2. There is no need to "start" dumpling or lightning
3. Make it clear that the "50 GB" is just a recommendation about when to use Dumpling/Lightning and when to use BR.
4. Format SQL statements so no horizontal scrolling is needed. Also use FORMAT_BYTES() instead of manual conversion to MiB. And remove the WHERE TABLE_SCHEMA=... to make the statements copy-pasteable.

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-11-23 02:54:46.329146879 +0000 UTC m=+459314.994373075: ☑️ agreed by hfxsd.
• 2023-11-23 03:33:21.995785823 +0000 UTC m=+461630.661012007: ☑️ agreed by Oreoxmt.

[hfxsd]

/approve

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.3: #15426.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.4: #15427.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #15428.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #15429.