Fix issues and documentation with integration tests after merge of #490. (#514)

* Fix explanation about containers images
* Add definitive URI to the containers images
* Document that new images must be set as public
* Add makefile options possible values
* Document that any mysql and mariadb tag can be use
* Add computation of docker_image path
* Refactor pre-command to separate commands for cleaner GHA output
* Refactor to use GHA test matrix
* Cut docker_image from documentation since it's now automatic
* Document how to use run_all_test.py to display the test matrix
* Temp: Add path to images in my fork to validate integrations tests

(cherry picked from commit e2aa655762)

test-containers/mysql-py38-mysqlclient201/Dockerfile

@@ -0,0 +1,21 @@
+FROM quay.io/ansible/ubuntu2004-test-container:main
+# ubuntu2004 comes with mysql-client-8
+
+# iproute2  # To grab docker network gateway address
+# python3.8-dev                # Reqs for mysqlclient
+# default-libmysqlclient-dev   # Reqs for mysqlclient
+# build-essential              # Reqs for mysqlclient
+RUN apt-get update -y && \
+    DEBIAN_FRONTEND=noninteractive apt-get upgrade -y --no-install-recommends && \
+    DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
+    python3.8 \
+    python3.8-dev \
+    mysql-client \
+    iproute2 \
+    default-libmysqlclient-dev \
+    build-essential
+
+RUN python3.8 -m pip install --disable-pip-version-check --no-cache-dir mysqlclient==2.0.1
+
+ENV container=docker
+CMD ["/sbin/init"]