Allocation-client subpage

[DO NOT MERGE] only for review
There is UserFactory, or even two factories in ralph.
So it's recommended way of creating test data.
Details:
 - https://github.com/allegro/ralph/blob/f98ff6abea86fcde106a24d203639c7f005d3361/src/ralph/util/tests/utils.py#L47
- https://github.com/allegro/ralph/blob/b3ea8e2557e0812570ed7a957bf5a712ae9a6720/src/ralph/ui/tests/global_utils.py#L107