Improve cost tracking capabilities

[ekzhu]

What feature would you like to be added?

• User should be able to understand LLM cost of an end to end run
• User should be able to track cost within a context (requires propagation between publishes. Look into how tracing is achieving this)
• User should be able to cancel a run early based on cost

Why is this needed?

API cost can be expensive and keep track of usage is important for production

[ekzhu]

This is completed with the addition of token-based termination condition (#4035) and token usage in messages #4017