[fix](regression) Make Iceberg rewrite where init script idempotent

[suxiaogang223]

What problem does this PR solve?

Issue Number: N/A

Problem Summary:

test_iceberg_rewrite_data_files_where_conditions depends on three Iceberg tables created by the Spark bootstrap script run21.sql. The script used CREATE TABLE IF NOT EXISTS and then always inserted the test rows. If the table already exists or the bootstrap SQL is re-entered after partial execution, the insert statements append data to the existing table, so the regression case may fail before running rewrite_data_files because COUNT(*) is no longer the expected 30 rows.

This PR makes the init SQL for this case idempotent by dropping and recreating the three test tables before inserting the fixed test data.

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
    • git diff --check -- docker/thirdparties/docker-compose/iceberg/scripts/create_preinstalled_scripts/iceberg/run21.sql
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes. The Iceberg bootstrap SQL now recreates the dedicated rewrite-where-condition test tables before loading fixed test data.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

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[suxiaogang223]

run buildall