eids missing in final spec ? Define recommendation spec for user.ext.eids

[abhinavsinha001]

There was a good standardisation proposal of how extended ids (eids) can be passed through oRTB in the draft/proposal : https://iabtechlab.com/wp-content/uploads/2017/09/OpenRTB-3.0-Draft-Framework-for-Public-Comment.pdf

Digitrust have also proposed using this standard in their oRTB spec: https://github.com/digi-trust/dt-cdn/wiki/OpenRTB-extension

Is there a reason why we ditched this in final release?

Looking at the growing adoption of identity solution:

• If there is no eids object in AdCOM user object then let's include some recommendation around structure which industry should use under user.ext
• This will help streamline implementations if we plan to include this later in spec

[abhinavsinha001]

Added PR-41 for adding this as official extension under 2.x - it has already been added to 3.x spec.