openEuler is the newest open source operating system, which is quite
famous and widely used in China. This patch aims to add the OS support
in kolla-ansible for the host OS.

bp: support-openeuler-os

Depends-On: https://review.opendev.org/c/openstack/ansible-collection-kolla/+/830320

Change-Id: I66dc84f02c324dbc0787ec25d4bd92ada9362e94

Depends-On: https://review.opendev.org/c/openstack/ansible-collection-kolla/+/831642
Change-Id: I70dcd2d0cade52a23b3e219b7e0aaa31193ec938

* add CentOS Stream 8 info & reno
* mark RHEL as deprecated in docs

Change-Id: Ifa3b8c7365e4092202bf9e89b67293cf8d983e0a

Change-Id: I8e3e0268faae871a197dc01d1c9447d00ef5d1e0

There is a time once every 2 years when ubuntu team releases new LTS
release. And then UCA joins with binary packages for current OpenStack
development cycle.

It is this time for Ubuntu 20.04 'focal'.

Includes CI fix to pass:

[CI] Temporarily block new Ansible

The proper fix [1] needs fixing older branches before newer.
This one allows to fix CI first, in the usual order.

To revert after [1] gets merged in all relevant branches.

[1] https://review.opendev.org/745648

Old-Change-Id: Ifbd37d8addd4322773118e2e9d46494741a8ae66
Related-Bug: #1891145

Depends-on: https://review.opendev.org/#/c/738994/


Change-Id: Ib8b70ee40ec2d19509cc84c0f530612f81907721
Co-Authored-By: Radosław Piliszek <radoslaw.piliszek@gmail.com>

Adds a support matrix page to documentation.

Change-Id: Ia783f7c42219617cde2accd3f1db013c9bda7679