Document more in detail the LDAP integration setup

[offtherailz]

Description

Actually https://mapstore.readthedocs.io/en/latest/developer-guide/integrations/users/ldap/ links to https://github.com/geosolutions-it/geostore/wiki/LDAP-Authentication but is not clear how to setup and how roles are assigned.
We have to improve the documentation.

Documentation section involved

• User Guide
• Developer Guide

Other useful information

[tdipisa]

@ale-cristofori could you please review this issue according to what is needed for c047 proj?

[ale-cristofori]

as a note, this ticket is linked to the more general merging of the Geostore documentation to the MapStore one we'd like to implement, as stated in this ticket