Improve featuring ElementPro

**Is your feature request related to a problem? Please describe.**

There are different places in element-admin where ESS Pro is mentioned. But it is not easy to get information about this.

**Describe the solution you'd like**
That should be linked to https://docs.element.io/latest/element-server-suite-pro/introduction-to-ess-pro/ or https://element.io/en/server-suite/pro

**Additional context**
A big reason for giving people element-admin as a gratis software is to give them a taste of what Element offers as a product.