fix: Exclude utilization checks for unallocated resources

[fregataa]

resolves https://github.com/lablup/giftbox/issues/592

When sessions(or kernels) are created without allocating cuda or any other devices, the value of kernel.occupied_slots field would be like below.

{'cpu': Decimal('1'), 'mem': Decimal('335544320')}

If we set thresholds of resources which are not in kernel.occupied_slots field to util checker, the checker determines the utilization with default 0 value resource. Example values below.

# utilization of a kernel
{'cpu': Decimal('1'), 'mem': Decimal('335544320'), 'cuda': 0}

# thresholds
{'cpu': Decimal('1'), 'mem': Decimal('10'), 'cuda': 2}

In this PR, util checker does not determine utilization of resources that is not in kernel.occupied_slots value.

Checklist: (if applicable)

• Milestone metadata specifying the target backport version
• Mention to the original issue
• Installer updates including:
  • Fixtures for db schema changes
  • New mandatory config options
• Test case(s) to:
  • Demonstrate the difference of before/after
  • Demonstrate the flow of abstract/conceptual models with a concrete implementation
• Documentation
  • Contents in the docs directory
  • docstrings in public interfaces and type annotations