fix(GraphQL): filter <> is Not_Contains instead of Not_Equal

[ghiscoding]

• while investigating for issue Filter for blanks / non blanks #1569, I found out that the GraphQL <> was set to be the equivalent of != but this is in fact false, since the <> is meant to represent Not_Contains while != is meant to represent Not_Equals and they both work differently since <> is for a substring but the != is for the entire string
• it is also related to the PR fix(filters): filters with != (not equal empty) should return non-blanks #1570
• Note that OData doesn't have a "Not Contains" query filter and so I only made the modification for GraphQL (OData has its own switch case for each operator)

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.8%. Comparing base (9837ef1) to head (3be073c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #1571    +/-   ##
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  Coverage    99.8%   99.8%            
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  Files         198     198            
  Lines       21731   21731            
  Branches     7278    7005   -273     
=======================================
  Hits        21670   21670            
  Misses         61      61            

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