📚 Documentation: Coolify installation instructions

[stnguyen90]

💭 Description

Update https://appwrite.io/docs/advanced/self-hosting to document how to install Appwrite using coolify, including any gotchas like _APP_VCS_GITHUB_PRIVATE_KEY.

👀 Have you spent some time to check if this issue has been raised before?

• I checked and didn't find similar issue

🏢 Have you read the Code of Conduct?

• I have read the Code of Conduct

[ChiragAgg5k]

I can work on this, can it be assigned to me?