Add vignette showing ODE model vectorisation

[pratikunterwegs]

This issue requests a vignette showing the upcoming functionality in #176. The vignette should include:

1. Passing infection parameters (and duration) as vectors;
2. Passing intervention and vaccination set lists;
3. Which model components are currently allowed to be passed as lists/vectors, and which are not (and whether vectorisation is intended in the future);
4. How to handle the output of vectorised model function calls.