feat(testing tool): add DEFINE/UNDEFINE statement support for ksqldb-testing-tool

[kancko]

Description

This changes allow define/undefine variables in test SQL files using DEFINE / UNDEFINE statement. It could be helpful in various cases, for example: when test sql file reuses main sql file (which relay on variables) via RUN SCRIPT.

Fixes: #9720

Testing done

Integration test cases were added under SqlTestingToolTest.

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")
• Do these changes have compatibility implications for rollback? If so, ensure that the ksql command version is bumped.

[confluent-cla-assistant]

🎉 All Contributor License Agreements have been signed. Ready to merge.
✅ kancko
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[JimGalasyn]

LGTM