[Access] select option in rest api causes invalid results

[UlyanaAndrukhiv]

Closes: #6056

Context

The issue in the select option for REST API calls was that the first result always returned as empty when the select key was the object with nested fields. Additionally, in such cases, other results after first were not filtered.

For example, the following case was not handled properly:

• full response: { "a": 1, "b": {"c":2, "d":3}},
• select=b,
• expected response after filtered: { "b": {"c":2, "d":3}}.

This PR updates how the select filter for REST API calls works in these scenarios and adds more functional tests to ensure proper functionality.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 41.48%. Comparing base (f4e316a) to head (7979b5a).

Files	Patch %	Lines
engine/access/rest/util/select_filter.go	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6300      +/-   ##
==========================================
- Coverage   41.49%   41.48%   -0.01%     
==========================================
  Files        2009     2009              
  Lines      143172   143175       +3     
==========================================
- Hits        59403    59398       -5     
- Misses      77587    77591       +4     
- Partials     6182     6186       +4     

Flag	Coverage Δ
unittests	41.48% <75.00%> (-0.01%)	⬇️

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[peterargue]

please add an explanation of what the bug was and how you fixed it to the PR description

[Guitarheroua]

Looks good to me!