Fix handling metadata filters with string values

[Nuvindu]

Purpose

$subject

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 77.20%. Comparing base (c5e5f48) to head (796f2b7).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
ballerina/utils.bal	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #16      +/-   ##
==========================================
+ Coverage   69.63%   77.20%   +7.56%     
==========================================
  Files           2        2              
  Lines         191      193       +2     
  Branches       68       69       +1     
==========================================
+ Hits          133      149      +16     
+ Misses         58       44      -14     

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