[admin] Move layout related components under layout/

[elia]

Summary

Those components were created in early times, now that we have a well defined system for organizing components we can make them fall under the same rule.

Checklist

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• I have written a thorough PR description.
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[codecov]

Codecov Report

Merging #5510 (e636fe0) into main (378ed49) will not change coverage.
Report is 13 commits behind head on main.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #5510   +/-   ##
=======================================
  Coverage   88.65%   88.65%           
=======================================
  Files         627      627           
  Lines       15037    15037           
=======================================
  Hits        13331    13331           
  Misses       1706     1706           

Files	Coverage Δ
...ponents/solidus_admin/layout/feedback/component.rb	100.00% <100.00%> (ø)
...lidus_admin/layout/navigation/account/component.rb	100.00% <100.00%> (ø)
...nents/solidus_admin/layout/navigation/component.rb	100.00% <100.00%> (ø)
.../solidus_admin/layout/navigation/item/component.rb	100.00% <100.00%> (ø)
...pp/components/solidus_admin/layout/page_helpers.rb	100.00% <ø> (ø)
...onents/solidus_admin/layout/skip_link/component.rb	100.00% <100.00%> (ø)

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