Add SLURM 'comment' field to RSC job metrics scuba table

[sju2]

Summary:
In this diff D98927579, we add --comment in the Slurm script for LCA training but the field is not currently exported from RSC to the scuba_fair_gpu_metrics Scuba table.

This enables ML Taxonomy use cases where --comment is used as a reliable source of truth for model type classification (e.g. lca_pretrain, lca_posttrain), since unlike --job-name, --comment cannot be overridden via CLI.

Changes:

• shelper/local.go: Added Comment field to SlurmMetadata and SlurmMetadataList structs
• shelper/slurm_helpers.go: Parse Comment from scontrol output in AttributeGPU2SlurmMetadata, aggregate in GetGPUData
• slurmprocessor/common.go: Added SlurmComment constant and wired into AddSlurmMetadataStr / AddSlurmMetadataSlice
• DCGM.thrift: Added comment dimension (field 117) to ODS3 schema
• Updated all test data files and test expectations

Post-land steps

1. Register the ODS3 schema — run this command to push the new comment dimension to ODS3:

buck2 run //monitoring/otel_gateway/ods3_client_schemas:DCGM_ods3-DCGM_ods3-register

2. fotel redeployment — the slurmprocessor runs inside fotel on each GPU node. Coordinate with the ai_pe_rsc oncall team to get fotel rebuilt and rolled out to RSC/AVA clusters. Until fotel is redeployed, the comment field will not be collected.

3. Once fotel is redeployed, the comment column will auto-appear in scuba_fair_gpu_metrics as data flows in — no separate Scuba schema change is needed.

Reviewed By: luccabb

Differential Revision: D103691035

[meta-codesync]

@sju2 has exported this pull request. If you are a Meta employee, you can view the originating Diff in D103691035.

[luccabb]

Review automatically exported from Phabricator review in Meta.

[luccabb]

this seems reasonable, comment is user input, so just be careful downstream with the cardinality increase on ODS3 tables

[github-actions]

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