[WIP] Cookbook initial lithosphere composition, plastic strain, temperature and topography

[anne-glerum]

This PR adds a cookbook that describes several plugins for creating initial conditions for setups of continental rifting.

For all pull requests:

• [x] I have followed the instructions for indenting my code.

For new features/models or changes of existing features:

• [x] I have tested my new feature locally to ensure it is correct.
• [ ] I have created a testcase for the new feature/benchmark in the tests/ directory.
• [ ] I have added a changelog entry in the doc/modules/changes directory that will inform other users of my change.