Add Concept Documentation for Changes feature

[rifont]

Path: /getting-started/concepts

Problem
We currently do not have a Changes section in the Concepts page.
We do however have a section for Changes under the Environments platform page. We can use this as a basis for creating the concept summary.

This feature is important for Organizations that seek to control deployment of features between test and production environment.

Scope
Given that the Concepts page is likely to be a commonly visited page, we should add the Changes section so that organizations assessing the viability of Novu can more easily determine feature availability.