Add 6.1.0 CHANGELOG entries (#1219)
Add 6.1.0 CHANGELOG entries (#1219)

This is probably missing some stuff, but is my edit of the initial list
compiled by Burak.

cr: da39a3ee5e6b4b0d3255bfef95601890afd80709@craigkerstiens
citusdata/citus,citusdata/citus,citusdata/citus,citusdata/citus,citusdata/citus