Add Organizations page under Platform

[rifont]

Problem
Organizations are a critical component in managing the complexity and segregation of multi-tenant and multi-department notification use-cases. We do not presently have a Platform section to highlight the key features of Organizations.

We do however have an Organizations page living under the Channels & Providers page. This can be used as a basis for creating a new standalone page.

Scope
Given that Organizations will be increasingly used by enterprise-size customers seeking to consume the Novu Platform, we should create a standalone page under https://docs.novu.co/platform/organizations

related: #368

[unicodeveloper]

I agree. However the related PR attached to this issue has to do with the API reference section alone.