Design and document how we triage issues

[kieferrm]

While the focus of #82032 is to bring our issue database back into a reasonable state, the purpose of this work item is to design and document a revised flow of how we triage issues so that we can keep the issue database in a reasonable state for longer.

[kieferrm]

The new flow has been documented in https://github.com/microsoft/vscode/wiki/Issues-Triaging.