6.6.0: Add release notes (#3511)
6.6.0: Add release notes (#3511)

Co-authored-by: Anthony Goddard <4834fbd4c8b9672428eaee651b9ff046eeafb7a7@gmail.com>
sensu/sensu-docs,sensu/sensu-docs,sensu/sensu-docs,sensu/sensu-docs,sensu/sensu-docs