Centralize Error Declarations

[wovalle]

Fireorm can throw different errors:

• Firestore errors: Mostly errors thrown by firebase-admin, they should be re-thrown back to the user
• Validation errors: If validateModels is true, fireorm run models validation on create and update. ValidationError is thrown.
• Other errors: Other errors that users might face. Usually are thrown new Error('Error text'). There are duplicated errors all over the codebase.

We have errors declarations all over the place and

Acceptance criteria:

• Refactor new Error()s in the codebase by creating errors in src/Errors
• Remove duplicated error declarations