Add release notes page for version 0.12.0

Patrole 0.12.0 has been released [1].
This commit adds a new page for 0.12.0 release notes.

[1] https://review.opendev.org/c/openstack/releases/+/783115

Change-Id: Ibbb1000d633372e2ca37b306fec3c284059905ba
2 files changed