[ABS] Use RUA Manager

To prevent API break issue, task-manager uses `rua_manager.h` instead of
`rua.h`.

Requires:
 - https://review.tizen.org/gerrit/#/c/platform/core/appfw/librua/+/209983/

Reference: submit/tizen_6.0/20201029.205505
Commit id: 6044f85ec6104dd3b3d3fd7b561d414ab221f87f
Requested by: None
SDK rootstrap version: 20201028_1