Improve documentation about ldap sync and timezones

[keguira]

In the documentation, we have the current statement :

In case the server hosting the LDAP directory is in a different timezone as GLPI, it is necessary to modify the Timezone variable to account for the difference.

In a lot of cases, it may be not an issue as it falls right but this can raise more questions but when you think about it, it's not that simple.

Use case 1 :

• a server configured as UTC or GMT with tzdata in database
• GLPI configured with a timezone Europe/Paris.
• An LDAP server on windows with a Europe/Paris timezone

Does the admin have to configure the LDAP with a timezone or keep GMT ?
As stated in the documentation, we should not change anything

Use case 2 (corner case) :

• a server configured as UTC or GMT with tzdata in database
• GLPI configured with a timezone Europe/Paris.
• An LDAP server on windows with a America/New-York timezone

Does the admin have to configure the LDAP with a timezone ? I suppose (GMT-4). But how to handle DST ? Manually ?
Note : this case is obviously exaggerated but in case of a worldwide use with multiple LDAP servers, it is not that stupid

Ask for clarifications :
This may be confusing : users tends to install GLPI without really taking care of this. Also, we do not have a clear understanding of why it is necessary and what are the impacts in case of a wrong configuration. Time management is not a simple thing and a clarification may be usefull.

Also, and i may raise another issue in the main project, we are not talking about the same thing everywhere : in some places we are talking in GMT and offset, in others we are talking about localized timezone (which implies the handling of DST)