Improve API documentation with query usages

[niveathika]

Purpose

All API doc except the batchExecute is updated with sample usage. batch Execute will need a code snippet.

Partially fixes ballerina-platform/ballerina-library#2524

Examples

N/A

Checklist

• Linked to an issue
• Updated the changelog
• Added tests

[codecov]

Codecov Report

Merging #155 (9a2a0cb) into main (9a5eee2) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #155   +/-   ##
=========================================
  Coverage     85.30%   85.30%           
  Complexity      182      182           
=========================================
  Files            16       16           
  Lines           633      633           
  Branches        139      139           
=========================================
  Hits            540      540           
  Misses           51       51           
  Partials         42       42           

Impacted Files	Coverage Δ
ballerina/client.bal	100.00% <ø> (ø)

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