Set default username for client connections

[kaneeldias]

Purpose

$subject

Related issue: ballerina-platform/ballerina-library#2397

Examples

Checklist

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

[codecov]

Codecov Report

Merging #456 (7eb8260) into master (a0fa761) will decrease coverage by 0.35%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #456      +/-   ##
============================================
- Coverage     91.03%   90.68%   -0.36%     
+ Complexity       40       39       -1     
============================================
  Files            13       13              
  Lines           279      279              
  Branches         45       45              
============================================
- Hits            254      253       -1     
  Misses           10       10              
- Partials         15       16       +1     

Impacted Files	Coverage Δ
ballerina/client.bal	97.14% <100.00%> (ø)
...erina/stdlib/mysql/nativeimpl/ClientProcessor.java	87.09% <0.00%> (-1.62%)	⬇️

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[github-actions]

This PR has been open for more than 15 days with no activity. This will be closed in 3 days unless the stale label is removed or commented.

[github-actions]

This PR has been open for more than 15 days with no activity. This will be closed in 3 days unless the stale label is removed or commented.

[daneshk]

LGTM