*: Forbid drop placement policy when it is in used by db or partition

[lcwangchao]

What problem does this PR solve?

Issue Number: close #27985

TODO: Add FT for dropping policy when it is used by partition after placement for partition finished

Check List

Tests

• Unit test

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• morgo
• xhebox

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[xhebox]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 8a06cf5

[AilinKid]

/merge

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