prep from metadata template checks for required fields

**Is your feature request related to a problem? Please describe.**
Prepping metadata results in a formatted list, but that list may not contain key terms. 

**Describe the solution you'd like**
Users should be alerted to the fact that some required metadata items are not present.

```
all(names(my_project_metadata_prepped) %in% wddsWizard::project_metadata_required_fields)
```