feat(config): add dynamic export controls to config command

[xieofxie]

Summary

Adds the dynamic export controls (--input-specs, --export-config, --dynamic-axes) to winml config, bringing it to parity with winml build / winml perf / winml export. This is a follow-up to #1083, which introduced these controls for build/perf and the shared cli_utils option/loader helpers.

What changed

• commands/config.py
  • Adds the three shared options (input_specs_option, export_config_option, dynamic_axes_option) and their params.
  • Loads a sparse override mapping via cli_utils.load_export_overrides (validates early, doesn't clobber auto-detected fields).
  • New _merge_export_overrides helper applies them via the shared merge_export_overrides, so --input-specs patches the auto-resolved input_tensors by name (unlisted inputs and their dtype/value_range preserved) and symbolic dims re-derive dynamic axes through WinMLExportConfig.__post_init__.
  • Wired into the single-config, --module list, and composite-pipeline paths.
  • Rejected for pre-exported ONNX inputs and for configs with export=null (clear UsageError).
  • Shows the provided files in the console summary; adds docstring examples.
• docs/commands/config.md: three new flag rows, an example, and a pitfall note.
• tests/unit/commands/test_config_cli.py: TestConfigExportControls — help visibility, override forwarding/parsing, no-op when absent, and ONNX rejection.

Verification

• ruff check + ruff format clean.
• tests/unit/commands/test_config_cli.py (55) and test_config_composite_resolution.py + test_config_value_priority.py (63) pass.
• Doc flag-alignment check passes.