docs(containers): add Bun application on Serverless Containers tutorial

[Slashgear]

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Description

This PR adds a new tutorial explaining how to deploy a Bun application on Scaleway Serverless Containers.

The tutorial follows the same structure as the existing Next.js and Django Serverless Containers tutorials:

• Create and test a Bun app locally using the native Bun.serve API
• Containerize the app with a Dockerfile based on the official oven/bun:1 image
• Build and push the image to the Scaleway Container Registry
• Deploy the container on Serverless Containers with recommended settings (port 3000, 500 mVCPU / 512 MB)

The intro highlights the synergy between Bun (fast startup, small memory footprint) and Serverless Containers (shorter cold starts, automatic scaling).

File added:

• tutorials/run-bun-serverless-containers/index.mdx