Add existing storage devices when preparing Switch inputs

# :rocket:

- [ ] Is your feature request essential for your project?

### Describe the workflow you want to enable
I wish a Grid object containing energy storage could be used to create Switch inputs, and the existing energy storage would be interpreted as a fixed investment like other existing generators. This was brought up in #101 but considered out of scope of that PR.

### Describe your proposed implementation
We probably want to change the call signatures of `build_generation_projects_info`, `build_gen_build_costs`, and `build_gen_build_predetermined` to take not only the `plant` dataframe, but a whole Grid, so that the information about existing storage devices can be added the the eventual output of these CSVs as well.