Data Modelling: Add dedicated section that curates all CrateDB specialities

[amotl]

About

We've identified a few resources that would better fit into a dedicated "data modeling" section.

References

• https://github.com/crate/tech-content/issues/143

/cc @kneth

[amotl]

There is a patch and a preview now, to present and discuss new guidance into that area and topics. Currently however, the content leaves something to be desired, so merging isn't quite around the corner just yet?

• Patch: Data modelling: Add new section (GenAI, unedited) #233
• Preview: https://cratedb-guide--233.org.readthedocs.build/start/modelling/