[FEATURE]: Rename relations to relationships

### Feature hasn't been suggested before.

- [x] I have verified this feature I'm about to request hasn't been suggested before.

### Describe the enhancement you want to request

When defining relationships between tables drizzle refers to that as 'relations'. In database theory a 'relation' is actually a set of tuples, so a table in SQL databases (https://en.wikipedia.org/wiki/Relation_(database)). To avoid any possible confusion 'relation' like it is used in drizzle should be renamed to relationship in code and documentation.