Upload exec_time explicitely, not in destructor (#5511)

Upload exec_time explicitely, not in destructor (#5511)

Since exec time is updated just in case of turned on profiler, no need
to upload it in a destructor. Moreover, since graph::Graph is reusable,
in its next usages BackendResolver will be recreated without destructing
JSON/ExecTime/Graph, so Backend, that is pointed by
JSON::_measurements.first in the first call is destructed and
JSON::uploadOperationsExecTime will cause a segmentation error in
`printString(backend.first->config()->id(), stream);`

Signed-off-by: Poshshoev Dilshodzhon <d.poshshoev@samsung.com>