clustering config to fork serve process for CPU core + load balancing

[aralroca]

Enhance the Brisa application by implementing a clustering configuration that utilizes the clustering property to improve performance and reliability by forking the process for each CPU core and load balancing requests.

This configuration should default to true in production on Linux, where load balancing is supported, and false in other environments unless explicitly enabled.

Note that this configuration is not applicable when using a Custom Server, and additional configuration may be required for Windows and macOS due to limitations in their handling of HTTP connection load balancing.