chore: changing description field to description json

[NarayanBavisetti]

Description

This PR renames the existing description field to description_json in both the Work Item and Page models. This change is required to introduce our new generic Description model, which will later expose a foreign key through the description field. Updating the existing key prevents naming conflicts and keeps the API consistent and readable. After this change, clients should start using description_json for the raw description data. The change is not backward compatible, so we will document the previous vs. new payload structure to assess external API impact.

Type of Change

• [x] Improvement (change that would cause existing functionality to not work as expected)