Categorise data types for Geo

In the limitations section of the documentation, we list out all of the data types that GitLab uses. https://docs.gitlab.com/ee/administration/geo/replication/#limitations-on-replicationverification Valery also helpfully provided more context to each which was captured in the Geo Discussion doc here: https://docs.google.com/document/d/18vGk6dQs7L0oGQOb_bNiFa5JhwLq5WBS7oNxQy09ml8/edit#heading=h.umcqkt7k7tic

We need to categorise these groups of data to help support building a framework for managing all data types with Geo.

The output of this issue should be updated documentation with a category column, along with further information added to the notes column.

For example,

Edited Nov 05, 2019 by Fabian Zimmer