Introduced `GetOrCreateCommandHandler` to handle `GetOrCreateCommand` requests.
The handler checks if an `Endpoint` with the specified `Uri` exists in the repository
and returns it if found. If not, it creates a new `Endpoint`, saves it, and returns
the newly created object. Added necessary `using` directives for repository abstraction
and Entity Framework Core functionality.
Introduced the `GetOrCreateCommand` class in the `ReC.Application.Endpoints.Commands` namespace. This class implements the `IRequest<Endpoint>` interface from MediatR to handle requests for retrieving or creating an `Endpoint`.
Added `Uri` property to the command with an `init` accessor for immutability. Included necessary `using` directives for `MediatR` and `ReC.Domain.Entities`.
