Add BigQuery cost profiling support and default parameters

[JunWang222]

This PR adds BigQuery cost profiling support, including:

• A BigQuery profiling pilot for running operator cost profiling locally
• Shared profiling documentation that explains how users can rerun profiling on their own machine
• BigQuery-specific setup notes and command examples
• Default BigQuery cost parameters for users who want to try Wayang with BigQuery

The default parameters are intended as starting values. For accurate optimization on a specific machine or deployment, users should follow the profiling guide and regenerate parameters locally.