feat: add FT.AGGREGATE to readonly commands

[chkp-omris]

Following !349

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (19e115b) 97.61% compared to head (6497005) 97.62%.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #351   +/-   ##
=======================================
  Coverage   97.61%   97.62%           
=======================================
  Files          76       76           
  Lines       30467    30467           
=======================================
+ Hits        29739    29742    +3     
+ Misses        613      611    -2     
+ Partials      115      114    -1     

Files Changed	Coverage Δ
internal/cmds/gen_search.go	93.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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