[Change request to #8170] Create endpoint for receiving total number of orders by employee

[ChernenkoVitaliy]

Description of a Change request:
Change functionality for endpoint /ubs/management/orders/count.
Now it returns a total number of orders.
Updated should returns total number of orders by employee.

Reason for Change:
The current endpoint will be used in the employee cabinet to receive the total number of orders by logged employees. The reason: every employee can be responsible for orders by such criteria as "Tarif", so the nimber of orders for every employee can be different.

Acceptance Criteria
The endpoint should return the total number of orders according to the logged employee.