Add PlantUML plan

[terhorstd]

Install PlantUML with a wrapper script to call from the command line. Can be used with sphinxcontrib.plantuml by adding the project dependency in pyproject.toml

[project.optional-dependencies]
doc = [
    # ...
    "sphinxcontrib-plantuml",
]

and configuring doc/conf.py:

extensions = [
    # ...
    "sphinxcontrib.plantuml",  # ref https://github.com/sphinx-contrib/plantuml/
]

plantuml = "plantuml"

Then documentation can be built with

module load plantuml
make html