[services] Rename PrimaryKey to PrimaryKeyDescriptor
Summary:
Depends on D3999
Raised in https://phabricator.ashoat.com/D3989#112043
Test Plan: Build the services
Reviewers: geekbrother, palys-swm
Reviewed By: geekbrother, palys-swm
Subscribers: ashoat, palys-swm, Adrian, atul, yayabosh
Differential Revision: https://phabricator.ashoat.com/D4013