DirSync support

[ma-ts]

I've been using this library with much success, and I've extended the library locally to add support for the DirSync control (https://learn.microsoft.com/en-us/previous-versions/windows/desktop/ldap/ldap-server-dirsync-oid).

This is very Microsoft-specific, and is not supported in many LDAP-servers. Would you be open to a contribution that adds support for this? And also: where would I then put this, given that this is a very vendored control.

[inejge]

I would prefer to keep vendor-specific controls outside of the base library -- I believe that so far all supported controls are based on standards or at least drafts. What I am definitely open to is supporting a custom control in a separate crate. Try to create ldap3-dirsync and report any problems here.