Installation docs lacking for dist / h2o-docs

[DieterDP-ng]

H2O version, Operating System and Environment
Branch jenkins-3.44.0.1, but likely affects current master as well (5620485c64aece7daeac46752d08533746dad762).
I am on Ubuntu 20.04.6 LTS.

Actual behavior
I receive build errors when running ./gradlew build dist -x test

Expected behavior
I get a smooth build.

Steps to reproduce

# Checkout jenkins-3.44.0.1
git checkout -b patchbuild jenkins-3.44.0.1
# install npm
nvm use --lts
# create an empty python venv
python -m venv /tmp/h2o-build-venv3
. /tmp/h2o-build-venv3/bin/activate
# install python dependencies listed in `README.md` and `h2o-docs/README.md`
pip install sphinx==2.1.1 sphinx_rtd_theme==0.2.4 recommonmark sphinx_prompt==1.1.0 sphinx-tabs==1.1.12 sphinx_substitution_extensions==2019.6.15.0 docutils==0.16 future "jinja2<3.1" grip tabulate requests wheel
# Build
export BUILD_HADOOP=1; ./gradlew build dist -x test -Pversion=3.44.0.1

Logs & suggested solution

Sphinx version error:
The sphinxcontrib.devhelp extension used by this project needs at least Sphinx v5.0; it therefore cannot be built with this version.
:buildH2oDevDist took 26.735 secs

> Task :buildH2oDevDist FAILED

Fix for this is described here

Error after applying this fix:

Sphinx version error:
The alabaster extension used by this project needs at least Sphinx v3.4; it therefore cannot be built with this version.
:buildH2oDevDist took 26.129 secs

> Task :buildH2oDevDist FAILED

Based on this google result, I tried adding "alabaster<0.7.14".

Next error:

Extension error:
Could not import extension numpydoc (exception: No module named 'numpydoc')
:buildH2oDevDist took 27.238 secs

> Task :buildH2oDevDist FAILED

Adding numpydoc to the depencies, results in a working build.

Additional context
I also suggest changing the pip install commands in the READMEs to list all dependencies in a single command rather one pip install per dependency. This ensures that pip can check version limitations of all dependencies as a whole, and is needed to get the above commands working.