Create additional default role descriptions unique to the demo_umami profile

Problem/Motivation

#256287: Give roles a description value is adding descriptions for the different roles on /admin/people/roles. For the roles created by the install profiles there is the need of having default descriptions. There is already an issue for the creation of the default role descriptions for the standard profile #3470972: Create default role descriptions for the standard profile. The roles in Umami slightly differ, content editor is dropped, while Author and Editor is being added.

Steps to reproduce

Proposed resolution

The ideation and discussion for the role description for the standard profile happens in: https://docs.google.com/document/d/1AIWUDvZugOizcdzboFZ34lgQOebpGHpWmzPn... within the standard profile section. The discussion about the two additional role descriptions, Author and Editor, should also happen in the aformementioned google docs within the Demo_Umami section at the bottom. Best either add new suggestions and or use the comment function leaving your thoughts about already added ones.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet