Python agent self-observability

[CodePrometheus]

In this proposal, I aim to implement the first version of self-observability for the Python agent. The general approach follows the issue, below are the specific details:

1. (created|finished)_(tracing|ignored)_context_counter - Counter. Due to forced sampling, there is currently no invocation within the agent's code. I'm still considering how to supplement this, so for now, no labels will be added here.
2. interceptor_error_counter - Counter. Maybe we could ignore the inter_type in python.
3. The meanings of possible_leaked_context_counter and tracing_context_performance remain unchanged.

[wu-sheng]

@kezhenxu94 Please take a look.

@CodePrometheus Anything I should pay attention. I am good for agent self-observability if it is just an implementation in Python.