add migration doc for model archive datastore setup

[chrisbc]

Explain use of CLI scripts to migrate archive and test that it's working.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.80%. Comparing base (d3d723c) to head (88f90ea).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #76   +/-   ##
=======================================
  Coverage   95.80%   95.80%           
=======================================
  Files          20       20           
  Lines        1143     1143           
  Branches       54       54           
=======================================
  Hits         1095     1095           
  Misses         34       34           
  Partials       14       14           

Flag	Coverage Δ
unittests	95.80% <ø> (ø)

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