ddl: Fix the storage instance may be physically dropped when the region is not removed

[JaySon-Huang]

What problem does this PR solve?

Issue Number: close #8710

Problem Summary:
There are some case that a region may not be removed from TiFlash when there are unhealth peers rule_checker @ pd. However, after the tiflash replica is set to zero, the data still be physically dropped after gc safepoint exceed.

What is changed and how it works?

• Prevent the storage instance being physically dropped when the region is not removed
  * Throw exception when the storage instance is not exist after schema synced

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Fix the issue that the tiflash replica data may be corrupted after setting the tiflash replica to 0 and add it back later

[JaySon-Huang]

/run-all-tests

[hongyunyan]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hongyunyan, Lloyd-Pottiger

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Needs approval from an approver in each of these files:

• OWNERS [Lloyd-Pottiger,hongyunyan]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-01-22 12:20:44.856149059 +0000 UTC m=+790486.420446763: ☑️ agreed by Lloyd-Pottiger.
• 2024-01-22 14:11:46.532058325 +0000 UTC m=+797148.096356029: ☑️ agreed by hongyunyan.

[JaySon-Huang]

/run-all-tests

[JaySon-Huang]

/hold

[JaySon-Huang]

/run-all-tests

[JaySon-Huang]

/run-unit-test

[JaySon-Huang]

/run-all-tests

[JaySon-Huang]

/unhold

[ti-chi-bot]

/cherry-pick release-7.5

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #8724.

[ti-chi-bot]

@ti-chi-bot: new pull request could not be created: failed to create pull request against pingcap/tiflash#release-7.5 from head ti-chi-bot:cherry-pick-8721-to-release-7.5: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-8721-to-release-7.5."}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request"}

In response to this:

/cherry-pick release-7.5

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[JaySon-Huang]

This PR also prevent data being unexpected dropped when the region is not removed. Ref #8777