update dependencies in pyproject toml to include sbi examples

[janfb]

Not all examples are currently executable using the dependencies specified in the pyproject.toml, e.g., the gravitational wave example has extra deps.

We should document this properly and add extra instrutions on how to get the grav wave code running, e.g., using a dependency group in the pyproject.toml or by creating an extra readme for that example.

[janfb]

see #5

TODO:

• give more precise instructions in README how to run the examples
• add optional dependency group, e.g., example, or per example, e.g., ddm, etc. to pyproject.toml