SCHED-921: Pass tf vars in json

[theyoprst]

Problem

Some tf var now contain quotes:

nvidia_admin_conf_lines = [
  "options nvidia NVreg_RestrictProfilingToAdminUsers=0", # Allow access to GPU counters in nsys profiler for non-root users
  "options nvidia NVreg_EnableStreamMemOPs=1",
+  "options nvidia NVreg_RegistryDwords=\"PeerMappingOverride=1;\"",
]

Because of that, terratest runs terraform with wrongly formatted vars:
-var nvidia_admin_conf_lines=["options nvidia NVreg_RestrictProfilingToAdminUsers=0", "options nvidia NVreg_EnableStreamMemOPs=1", "options nvidia NVreg_RegistryDwords="PeerMappingOverride=1;""]

And it leads to terraform errors:

TestTerraformDestroy 2026-02-10T08:16:15Z logger.go:67: Error: Missing item separator
TestTerraformDestroy 2026-02-10T08:16:15Z logger.go:67: 
TestTerraformDestroy 2026-02-10T08:16:15Z logger.go:67:   on <value for var.nvidia_admin_conf_lines> line 1:
TestTerraformDestroy 2026-02-10T08:16:15Z logger.go:67:   (source code not available)
TestTerraformDestroy 2026-02-10T08:16:15Z logger.go:67: 
TestTerraformDestroy 2026-02-10T08:16:15Z logger.go:67: Expected a comma to mark the beginning of the next item.

Solution

Pass vars as a JSON, which already does proper escaping.

Testing

https://github.com/nebius/soperator/actions/runs/21860154458/job/63086857937
(cancelled after successful passed the problematic point)