feat(stirling-pdf) add stirling-pdf

[xstar97]

Description
add stirling-pdf to incubator
⚒️ Fixes #

⚙️ Type of change

• ⚙️ Feature/App addition
• 🪛 Bugfix
• ⚠️ Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 🔃 Refactor of current code

🧪 How Has This Been Tested?

📃 Notes:

✔️ Checklist:

• ⚖️ My code follows the style guidelines of this project
• 👀 I have performed a self-review of my own code
• #️⃣ I have commented my code, particularly in hard-to-understand areas
• 📄 I have made corresponding changes to the documentation
• ⚠️ My changes generate no new warnings
• 🧪 I have added tests to this description that prove my fix is effective or that my feature works
• ⬆️ I increased versions for any altered app according to semantic versioning
• I made sure the title starts with feat(chart-name):, fix(chart-name): or chore(chart-name):

➕ App addition

If this PR is an app addition please make sure you have done the following.

• 🖼️ I have added an icon in the Chart's root directory called icon.png

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