docs(telemetry): add instrumentation conventions, align telemetry to them #2994

Job	Run time
Lint	1m 28s
Unit Test (Linux, Electron 37)	1m 1s
Integration Test (Linux, VS Code stable)	48s
Integration Test (macOS, VS Code stable)	1m 11s
Package	33s
Unit Test (Windows, Electron 42.3.0)	2m 54s
Chromatic	38s
Integration Test (Linux, VS Code 1.105.0)	52s
Integration Test (Windows, VS Code stable)	2m 28s
Unit Test (macOS, Electron 42.3.0)	1m 38s
Unit Test (Linux, Electron 42.3.0)	1m 3s
	14m 34s

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