refactor: toggle for negative item rates in Selling Settings

[ruthra-kumar]

There are some customers who use negative rates and want that option. Adding a checkbox in Selling settings to make it configurable.

continues: #36027

[codecov]

Codecov Report

Merging #36642 (a0fc685) into develop (539cfd0) will increase coverage by 0.05%.
Report is 15 commits behind head on develop.
The diff coverage is 100.00%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #36642      +/-   ##
===========================================
+ Coverage    64.77%   64.82%   +0.05%     
===========================================
  Files          792      792              
  Lines        61779    61798      +19     
===========================================
+ Hits         40018    40063      +45     
+ Misses       21761    21735      -26     

Files Changed	Coverage Δ
erpnext/accounts/report/financial_statements.py	80.42% <ø> (ø)
...xt/accounts/doctype/payment_entry/payment_entry.py	83.71% <100.00%> (-0.09%)	⬇️
.../report/accounts_receivable/accounts_receivable.py	71.11% <100.00%> (+0.05%)	⬆️
erpnext/controllers/status_updater.py	88.42% <100.00%> (+0.06%)	⬆️

... and 7 files with indirect coverage changes

[tdci]

the toggle should be the other way around.
the option should be the on customer that do not want a negative rate "Disable negative rates for items" on their invoices.
this should not break anything prior to the last push.

[tukutela]

Thankyou!!!!!