[Feat]: Allow disabling Telemetry via environment variable

[minimAluminiumalism]

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

Currently, a2a-sdk automatically enables telemetry instrumentation if the opentelemetry package is detected in the python environment.
In some scenarios, a user might have opentelemetry installed for other libraries or the main application, but they may not want a2a-sdk to generate spans. There is currently no way to disable a2a-sdk telemetry without uninstalling the opentelemetry package, which is not feasible if other parts of the application depend on it.

Describe the solution you'd like

Introduce an environment variable (e.g., A2A_ENABLE_TELEMETRY or A2A_DISABLE_TELEMETRY) to explicitly control the enabling of telemetry instrumentation.

Describe alternatives you've considered

No response

Additional context

The logic resides in src/a2a/utils/telemetry.py. It currently only checks for ImportError.

Code of Conduct

• I agree to follow this project's Code of Conduct

[saravana-tk]

Hi, I would like to work on this. Can you assign it to me?

[minimAluminiumalism]

Hi, I would like to work on this. Can you assign it to me?

I've found a similar issue #604 and there is already a PR, so I'll close this.