Add clicko migration tool to schema management documentation

[arsura]

Expanded the section on imperative schema management tools to include clicko, detailing its features, benefits for ClickHouse users, and considerations for use. Updated examples to reflect this addition.

Summary

Added clicko to knowledgebase/schema_migration_tools.md as a recommended imperative migration tool. clicko is designed specifically for ClickHouse with support for custom table engines, insert quorum, and cluster-aware DDL — making it a better fit for self-hosted sharded deployments compared to general-purpose runners like Goose or golang-migrate.

Checklist

• Delete items not relevant to your PR
• URL changes should add a redirect to the old URL via https://github.com/ClickHouse/clickhouse-docs/blob/main/docusaurus.config.js
• If adding a new integration page, also add an entry to the integrations list here: https://github.com/ClickHouse/clickhouse-docs/blob/main/docs/integrations/index.mdx

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