ddl/ingest: create new local backend if necessary (#44140)

[ti-chi-bot]

This is an automated cherry-pick of #44140

What problem does this PR solve?

Issue Number: close #44137, close #44044

Problem Summary:

See #44137 (comment).

What is changed and how it works?

If there is no writers in engine, it means the local backend is closed.

• Reopen the local backend before retrying adding index.
• Skip deleting SST files that belong to a running DDL job.

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

Please refer to Release Notes Language Style Guide to write a quality release note.

None

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[tiancaiamao]

Please resolve conflict @tangenta

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: tiancaiamao, wjhuang2016

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-07-07 06:22:49.223666353 +0000 UTC m=+53860.994005066: ☑️ agreed by wjhuang2016.
• 2023-07-07 06:26:59.794171209 +0000 UTC m=+54111.564509922: ☑️ agreed by tiancaiamao.