12,400+ of "unknown files" are ".xz" - Mark them appropriately

[raprasad]

12,400+ of "unknown files" (9.990% of unknown files) have extension .xz

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Fixes:

• Now: Mark these as compressed files instead of unknown.
• By end of year: Alternately, re-crawl these files and save the file list as metadata
  • Depends on prototype json schema endpoints for file metadata (sloan project) #3088

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Filed under: tech debt

---

  "data": {
    "number_unique_extensions": 1454,
    "file_extension_counts": [
      {
        "extension": "",
        "count": 36657,
        "total_count": 124357,
        "percent_string": "29.477%"
      },
      {
        "extension": ".xz",
        "count": 12423,
        "total_count": 124357,
        "percent_string": "9.990%"
      },
  (etc)

[mheppler]

Related to #2202

[pdurbin]

Closing in favor of #2202