Handle arbitrary action IDs.

Created by: todo[bot]

https://github.com/sourcegraph/sourcegraph/blob/2958bbecf228bec285cffbd1f45ec1b1dd969ac4/browser/src/shared/tracking/eventLogger.tsx#L82-L87

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This issue was generated by todo based on a @todo comment in 2958bbecf228bec285cffbd1f45ec1b1dd969ac4 when #3903 was merged. cc @sourcegraph.