Add list of acknowledgments to release notes

This contains all individuals mentioned in the commit messages during
PostgreSQL 10 development.

current through babf18579455e85269ad75e1ddb03f34138f77b6

Discussion: https://www.postgresql.org/message-id/flat/54ad0e42-770e-dfe1-123e-bce9361ad452%402ndquadrant.com