Telemetry: coder.exportTelemetry command (JSON array and OTLP/JSON)

[EhabY]

Part of the Telemetry Phase A rollout. See the RFC in Linear: AIGOV-154.

Scope

• Register the coder.exportTelemetry command via the dispatcher from ENG-2458.
• Date range selection via QuickPick with presets ("Last 24 hours", "Last 7 days", "Last 30 days", "All time", "Custom range…"). Custom range falls back to two InputBox prompts with validateInput for YYYY-MM-DD dates.
• File filtering by filename only, since daily files are date-stamped. No file contents are opened outside the selected range.
• Format selection via a second QuickPick:
  • JSON array (default): a single JSON document for human inspection or compliance review.
  • OTLP/JSON: OpenTelemetry Logs data model wrapped in { "resourceLogs": [...] }. Resource attributes are lifted from the stored context; each event becomes one LogRecord with body, attributes, and observedTimeUnixNano. Can be POSTed unchanged to any OTLP/HTTP endpoint.
• Streaming output via readline.createInterface + createReadStream. Memory usage stays proportional to a single line, not total file size.
• vscode.window.showSaveDialog with suggested filename coder-telemetry-{range}.{ext} and a filter matching the chosen format.

Tests

• Unit tests for date range parsing and the filename-based file filter.
• Unit tests for the JSON-array writer (header, comma-separated lines, footer).
• Unit tests for the OTLP/JSON writer (envelope structure, LogRecord shape, resource attribute mapping from context).
• Memfs-backed integration test that seeds a few JSONL files, exports a range, and verifies the output.

Out of scope

• No Prometheus endpoint. Prometheus cannot ingest event files directly. Users who want Prometheus feed the OTLP/JSON output into an OTel Collector and let it forward via the prometheusremotewrite exporter.

Depends on AIGOV-243, AIGOV-244, ENG-2458.