[Feature] Add employees model, fix timestamps, and add common fields

### Is there an existing feature request for this?

- [X] I have searched the existing issues

### Describe the Feature

This is a FR created retroactively to correspond to a customer-created [PR](https://github.com/fivetran/dbt_netsuite_source/pull/54) so we can track it internally.

- Employee model: Add an employees staging model to include fields like "Name" and "Supervisor" in downstream models.
- Timestamp Conversion Fix: Cast timestamp fields as dates to prevent timezone conversion issues in reporting tools.
- Field Enrichment: Add commonly used fields to key models

### Describe alternatives you've considered

_No response_

### Are you interested in contributing this feature?

- [ ] Yes.
- [ ] Yes, but I will probably need assistance.
- [ ] No.

### Anything else?

_No response_