[Feat]: Telemetry to collect anonymous A2A usage across all SDK

### Is your feature request related to a problem? Please describe.

It is nearly impossible to measure adoption of A2A.

Github stars and SDK downloads are the only metrics we have.

**Ideal metrics:**

- Monthly Active Agents using A2A (have had any iteractions)
- Monthly sum of A2A tasks

Metric dimensions (MECE):

- Breakdown by A2A task terminal status
- Breakdown by client/server
- Breakdown by SDK language and version number
- Breakdown by data binding or transport

Optional Metric dimensions (MECE):

- Breakdown by company names (domains)
- Breakdown by agent card attributes

### Describe the solution you'd like

**Recommendation:**

https://about.scarf.sh/post/the-open-source-business-metrics-guide

NOTE: I would be fine with any solution which solved the aggregate anonymous metrics needs, this is what https://copilotkit.ai uses and seems sufficient.

**Concerns:**

- transparency (default on but opt-out)
- privacy (must not accidentally collect sensitive data)
- latency and performance (must not slow down execution)

Other open source projects have adopted 3rd party telemetry providers, and I am only recommending we adopt a path which does pass legal review as described in this policy:

https://www.linuxfoundation.org/legal/telemetry-data-policy

### Describe alternatives you've considered

- Google Analytics (too much data collection)
- no metrics (not helpful)

### Additional context

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct