Changelog for 1.6.9, 1.6.10, and 1.7.0 (#6075)

* Update CHANGELOG for 1.6.9 stable release.

* [WIP] Prepare CHANGELOG for 1.7.0 beta release.

* Contract warp

* Update changes for 1.7.0

* Update description for 1.7.0 in changelog

* Update Changelog for 1.7.0 beta and 1.6.10 stable

* Address reviews for the Changelog.

* Fix blog URL in changelog.

* Fix typo in Changelog.

* Update changelog for 1.7.0 beta and 1.6.10 stable