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### What does this PR do?

Adds `gpu_nvlink_capable` and `gpu_nvlink_version` tags to GPU metrics.

### Motivation

Knowing whether a GPU is NVlink-capable and the version of the NVlink system or not is useful to ensure the presence of certain metrics and to compare GPU performance.

Another PR will also use part of this code to allow segmenting telemetry based on NVLink capability. 

### Describe how you validated your changes

Unit tests, manually validated in nvlink-enabled instance.

### Additional Notes

Both tags might be slightly redundant but having two doesn't cost extra cardinality (gpu_uuid is already there, with one value per GPU) and it allows separating "nvlink GPUs/non nvlink GPUs" and between specific versions.

This PR also updates the metric specification to ensure that the NVlink capablity reported in the spec and the one reported by NVML are consistent.

Co-authored-by: guillermo.julian <guillermo.julian@datadoghq.com>