Add support for setting libcuda verbosity

[4gt-104]

What type of PR is this?
/kind feature

What this PR does / why we need it:
Add support for setting LIBCUDA_LOG_LEVEL during admission.

Which issue(s) this PR fixes:
Resolves: #544

Special notes for your reviewer:
I added a new function, setOrUpdateEnvVar, as I couldn’t find an existing alternative in the source code. However, I believe it should be placed in a more accessible location other than pkg/device/nvidia/device.go.

Does this PR introduce a user-facing change?:
Default log level stays the same.
Users should upgrade their values.yaml files if they want to change verbosity level.

[codecov]

Codecov Report

Attention: Patch coverage is 47.05882% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/device/nvidia/device.go	47.05%	8 Missing and 1 partial ⚠️

Flag	Coverage Δ
unittests	27.10% <47.05%> (+0.19%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
pkg/device/nvidia/device.go	33.94% <47.05%> (+2.36%)	⬆️