docs: add plantuml and use virtual environment to generate docs

Documentation generator can be run inside Python virtual environment.
This allows to isolate from the system-wide changes and add Sphinx
extensions that aren't packaged in a distribution.

The only exception right now is plantuml package. We rely on plantuml to
generate diagrams and since it is written in Java, it cannot be
installed directly into the Python venv through 'pip' tool.

Fixes: https://pagure.io/freeipa/issue/9148

Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Francisco Trivino <ftrivino@redhat.com>

freeipa.spec.in

@@ -323,7 +323,9 @@ BuildRequires:  python3-wheel
 
 %if %{with doc}
 BuildRequires: python3-sphinx
-BuildRequires: python3-m2r
+BuildRequires: plantuml
+BuildRequires: fontconfig
+BuildRequires: google-noto-sans-vf-fonts
 %endif
 
 #

ipatests/azure/templates/build-docs-fedora.yml

@@ -1,6 +1,8 @@
 steps:
 - script: |
     set -e
-    echo "Building documentation"
+    echo "Generate virtual environment for building documentation"
+    make -C doc/ venv
+    echo "Build documentation"
     make -C doc/ html
   displayName: Build documentation