Fix autogeneration of documentation

[tim-vd-aardweg]

What is the need for this task.
It seems that HYDROLIB-core 0.5.2. was the last release where the documentation was still successfully auto-generated. After that, it did not run successfully anymore. We should fix this.

GitHub actions give the following messages:

Material emoji logic has been officially moved into mkdocs-material
version 9.4. Please use Material's 'material.extensions.emoji.twemoji'
instead of 'materialx.emoji.twemoji' in your 'mkdocs.yml' file.


markdown_extensions:
  - pymdownx.emoji:
      emoji_index: !!python/name:material.extensions.emoji.twemoji
      emoji_generator: !!python/name:material.extensions.emoji.to_svg


'mkdocs_material_extensions' is deprecated and will no longer be
supported moving forward. This is the last release.

error: No module named 'mkdocs.tests'

It will probably involve updating dependencies, such as:

• mkdocs-material = "^9.4"
• mkdocstrings = "^0.22"
• mkdocstrings-python = "^0.6.0"
• mkdocs-autorefs = "^0.4"
• pymdown-extensions = "^10.0"
• jinja2 = "<4"
• mkdocs-jupyter = "^0.24.8"

and updating the mkdocs.yml:
emoji_index: !!python/name:material.extensions.emoji.twemoji