Chore/cleanup dockerfiles and workflows

[fyzanshaik-atlan]

✨ Description

1. Fix Sphinx docs workflow - Replaced sphinx-notes/pages@v3 with explicit uv sync --group docs to properly install pyatlan before building docs
2. Rename Dockerfile - Renamed Dockerfile.chainguard to Dockerfile since it's now the only Dockerfile

Jira link: N/A

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🧩 Type of change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• 🔄 Refactor (code change that neither fixes a bug nor adds a feature)
• 🧹 Maintenance (chores, cleanup, minor improvements)

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✅ How has this been tested?

• Verified docs build locally: uv sync --group docs && uv run sphinx-build -b html docs docs/_build
• Verified Dockerfile rename is reflected in workflow

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📋 Checklist

• My code follows the project's style guidelines
• I've performed a self-review of my code
• I've updated the documentation as needed
• There are no new warnings from my changes

[Aryamanz29]

LGTM - thanks! @fyzanshaik-atlan 🚀