refactor: add DatabaseMeta.gc_in_progress

[drmingdrmer]

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Summary

refactor: add DatabaseMeta.gc_in_progress

If gc_in_progress is set, no un-drop can be done on this database. Because the related data may already have been deleted.

This commit does not use this flag yet, and will be used in next commit.

• Part of #16433

Tests

• [x] Unit Test
• [ ] Logic Test
• [ ] Benchmark Test
• [ ] No Test - Explain why

Type of change

• [x] Refactoring

Related Issues

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This change is