Update custom data skill template

[Ruuudy1]

Moves and reworks the custom-data skill work from QuantConnect/Agent-Skills-and-Workflows#18 into the Documentation skill-template convention.

Changes:

• Updates skill-templates/importing-data/custom-data/SKILL.md in place.
• Keeps the template self-contained for the Documentation bundler.
• Uses the Lean CLI directly for Cloud Object Store uploads with lean cloud object-store set <key> <path>.
• Keeps dual Python and C# guidance through py / cs markers.
• Adds explicit JSON-array / unfolding collection guidance for Object Store data.
• Documents keeping JSON array files as one-line/minified JSON under the requested Object Store key.
• Shows minimal Python and C# FileFormat.UNFOLDING_COLLECTION / FileFormat.UnfoldingCollection patterns that return sorted BaseDataCollection objects.
• Adds guardrails to preserve the user's trading rule and report condition pass counts instead of relaxing strategy logic when data loads but orders are 0.

Validation:

• python skill-templates\\bundle-skills.py
• Checked generated Python and C# custom-data skills for the JSON-array guidance.
• python skill-templates\\bundle-skills.py --validate-only