[FIX] SQL: Fix the issue with database collation setting when retrieving column values

[PrimozGodec]

Issue

The database can have different collation settings (how to compare characters in the group by, distinct, ...). It has an impact on values we get when we retrieve all distinct values from column to create a discrete variable. If a collation is Latin it ignores utf8 characters, it can even be case insensitive. When creating variable we still want to have all possible values in the column since later when we retrieve actual data for a table (SELECT * FROM Table) we get values as they are (collation does not have an effect).

Description of changes

This PR implements a workaround for GROUP BY in cases when we want all values to create a variable.

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #5089 (bcdb587) into master (81ccf30) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #5089      +/-   ##
==========================================
+ Coverage   84.65%   84.74%   +0.08%     
==========================================
  Files         285      286       +1     
  Lines       59541    60043     +502     
==========================================
+ Hits        50406    50884     +478     
- Misses       9135     9159      +24