fix(application): allow both placement and constraints together.

Some constraints and placement details can conflict with each other but
not all. Specifying memory size and to use a specific machine doesn't
work. Spaces and placement can coexist however.

Let the jujud decide how to resolve conflicts between placement and
constraints.

internal/provider/resource_machine.go

@@ -181,7 +181,6 @@ func (r *machineResource) Schema(_ context.Context, req resource.SchemaRequest,
 				Validators: []validator.String{
 					stringvalidator.ConflictsWith(path.Expressions{
 						path.MatchRoot(SSHAddressKey),
-						path.MatchRoot(ConstraintsKey),
 					}...),
 				},
 			},