Add 'Known Limitations' back to GraphQL v2 Data Modeling docs

[djsjr]

Is your feature request related to a problem? Please describe. I tried using @searchable with DataStore because the incompatibility was not mentioned in the new v2 docs. The Known Limitations section is present in the legacy docs and mentions this incompatibility.

Describe the solution you'd like Add known limitations section, or make it compatible.

Describe alternatives you've considered I checked the legacy docs.

Additional context n/a