Account for SCD in telemetry reports

[pmalek]

Problem statement

KIC uses a phone home mechanism through anonymous reports (relevant CLI flag is called: anonymous-reports).

Given we've introduced an SCD feature, we should report in the telemetry whether the feature is turned on or not.

Related issues

#702

Acceptance critieria

• a telemetry label exists that says whether SCD is in use and how many instances are managed

[czeslavo]

I've extracted an issue for handling telemetry of multiple gateways when we allow using heterogenous Kong versions/dbmodes. In 2.9 we're going to support only homogenous configurations. #3589