Documentation feedback on /docs/feature/query: Educate readers about the power of CTEs

### Documentation feedback

- Page title: Advanced Querying
- Page URL: https://cratedb.com/docs/guide/feature/query/index.html
- Source: https://github.com/crate/cratedb-guide/blob/main/docs/feature/query/index.md

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Via this dbt page, I just visited the PostgreSQL documentation about CTEs.

- https://github.com/dbt-labs/docs.getdbt.com/discussions/1787
- [PostgreSQL Common Table Expressions](https://www.postgresql.org/docs/15/queries-with.html)

I think the PostgreSQL page bears a few sweet examples that could also be used on our documentation page. Let me know what you think about it, and/or if you know about any other sensible pieces from your workbenches to include here, particularly about CTEs.

/cc @kneth, @surister, @simonprickett, @hammerhead, @hlcianfagna, @wierdvanderhaar