Add `_include` pages to `sitemap_excludes` to avoid duplicate content and "empty" search results

### Documentation feedback

Pages that get included via `:::{include}` (e.g. `https://cratedb.com/docs/guide/_include/card/timeseries-dask.html`) are also visible in the [sitemap](https://cratedb.com/docs/guide/site.xml), can we add them to `sitemap_excludes` for those pages so they don't show up (and thus also not show in search)?

- Page title: Time Series Fundamentals with CrateDB
- Page URL: https://cratedb.com/docs/guide/domain/timeseries/fundamentals.html
- Source: https://github.com/crate/cratedb-guide/blob/main/docs/domain/timeseries/fundamentals.md

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