handle objectguid endianness

[butonic]

Active Directory stores objectGUID with mixed endianness:

• The first 3 components (time-low, time-mid, time-high) are stored in little-endian
• The last 2 components (clock-seq and node) are stored in big-endian

When the attribute is 'objectguid' (and IDIsOctetString==true) we now swap the byte order for the first three components before encoding.

[butonic]

I'll update this to align with the implementation in https://github.com/opencloud-eu/opencloud/blob/main/services/graph/pkg/identity/ldap.go