Add doc test CI workflow reusing existing model job infrastructure

[ydshieh]

Summary

• Add two optional, backward-compatible inputs (test_path_prefix, test_file_suffix) to model_jobs.yml and self-scheduled.yml — defaults preserve all existing behavior
• Extend the set-matrix step in self-scheduled.yml to discover runnable doc examples (files containing ```py runnable) when test_file_suffix is set, emitting one single-element slice per model so each model's doc tests run in a separate parallel job
• Add self-doc-scheduled-caller.yml — a new daily caller that passes job: run_models_gpu with test_path_prefix: docs/source/en/model_doc and test_file_suffix: .md, reusing all existing Slack reporting, failure checking, and artifact infrastructure from self-scheduled.yml without duplicating any workflow files

Test plan

• Trigger manually via workflow_dispatch on self-doc-scheduled-caller.yml
• Or push to a branch matching run_doc_tests* to trigger the caller
• Verify one job per model doc file is spawned in the run_models_gpu matrix
• Verify existing model CI (self-scheduled-caller.yml) is unaffected (all new inputs are optional with defaults)

🤖 Generated with Claude Code

[HuggingFaceDocBuilderDev]

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