There is an incompatibility issue between the sphinx version in Ubuntu
focal and the docutils version pulled in by sphinx-tabs. We need to make
sure that pip doesn't pull in a version of docutils that would break
sphinx:

https://github.com/sphinx-doc/sphinx/issues/9841



Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

The Ubuntu version we downgraded to doesn't have support for
sphinx-tabs. Switch that to pip until we can upgrade to 22.04.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

The currently used version, impish, is not updatable anymore since July
the 14th and we don't have a newer version in our repository. Downgrade
this to focal to fix the container image builds.

Fixes: #724


Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

The docs will contains lfs blobs so make sure the tooling is in place.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

The CI system depends on a number of containers. Those used to be
defined in another repository but with this migration we can now
simplify and aggregate everything into one repository.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>