Feedback on /integrate: Introduce categories or groups

### Documentation feedback

- Page title: Integrations
- Page URL: https://cratedb.com/docs/guide/integrate/index.html
- Source: https://github.com/crate/cratedb-guide/blob/main/docs/integrate/index.md

---

Having the TOC with a long list of alphabetical list integrations is not very practical to navigate.

I would suggest to swap the grouping, so that the TOC consists of the Categories and then the integrations under that.
Should an integration below to more than one category, the integration would be located under it's "primary" category and linked to from the other categories.

- Integrations
- Cat A (Page as now with links to 1, 2)
- Integration 1
- Integration 2

- Cat B (Page as now with link to 3, 4, and 1 (which belongs to Cat A and B))
- Integration 3
- Integration 4