Create a Development Container Feature for Dev Proxy

To make it easier for developers to integrate Dev Proxy into GitHub Codespaces and VS Code Dev Containers, we should create a [Development Container Feature](https://containers.dev/implementors/features/) for Dev Proxy.

**Benefits of this approach:**
- **Streamlined setup:** Developers can enable Dev Proxy with a single line of configuration in their `devcontainer.json`, avoiding manual installation steps.
- **Consistency:** Ensures consistent Dev Proxy installation and configuration across different environments and teams.
- **Reusability:** The feature can be reused across multiple dev containers and projects, reducing duplicate effort.
- **Discoverability:** Features are listed in the Dev Container Feature marketplace, making Dev Proxy easier to find and adopt.
- **Best practices:** Follows the recommended approach for extensibility in Codespaces and Dev Containers.

A GitHub repository template is available to author the feature: [@devcontainers/feature-starter](https://github.com/devcontainers/feature-starter)

[VSCode Docs: Dev Container Features](https://code.visualstudio.com/docs/devcontainers/containers#_dev-container-features)

Beginnen Sie mit der Repository-Vorlage @devcontainers/feature-starter und der verlinkten Dokumentation zu Development Container Features und VS Code. Definieren Sie das Feature so, dass Dev Proxy mit einer einzigen devcontainer.json-Konfigurationszeile aktiviert werden kann, und überprüfen Sie anschließend, dass das resultierende Feature wiederverwendbar und für die Aufnahme in den Marketplace geeignet ist.

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