[docs] Enforce the same lest pane template in sphinx config

[aobolensk]

Solve the problem when part of ToC disappears on the left pane on some pages

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.94%. Comparing base (f1d983a) to head (00b8788).
Report is 59 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #316   +/-   ##
=======================================
  Coverage   93.94%   93.94%           
=======================================
  Files          26       26           
  Lines         479      479           
  Branches      143      143           
=======================================
  Hits          450      450           
  Misses         14       14           
  Partials       15       15           

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