[DOC] update missing data imputation docs

[solegalli]

Swap the api by the user guide files, as details should go in the user guide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.27%. Comparing base (647e736) to head (a035782).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #903   +/-   ##
=======================================
  Coverage   98.27%   98.27%           
=======================================
  Files         116      116           
  Lines        4978     4978           
  Branches      795      795           
=======================================
  Hits         4892     4892           
  Misses         55       55           
  Partials       31       31           

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