Improve telemetry ergonomics/perf

The telemetry service implementation is more strict than it's interface suggests. Some ideas: * (ergo) have a stricter spec for the event-name of `publicLog`, e.g only allow lower-case characters, don't allow numbers (AFAIK they are ignored /cc @hediet) * (ergo)(lint-rule) only allow static strings, no interpolation * (perf) spec that the data in modified/cleansed in-place. This will save us from copying tons of data and I believe no user of telemetry re-uses the payload