Replace slack channel link with discord server link

[aashikam]

Purpose

ballerina-platform/ballerina-library#3463

Module does not have a spec.md

Checklist

• Linked to an issue
• Updated the changelog
• Added tests
• Updated the spec
• Checked native-image compatibility

[codecov]

Codecov Report

Base: 80.84% // Head: 80.89% // Increases project coverage by +0.05% 🎉

Coverage data is based on head (5dbe878) compared to base (7355fb8).
Patch has no changes to coverable lines.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #310      +/-   ##
============================================
+ Coverage     80.84%   80.89%   +0.05%     
  Complexity      107      107              
============================================
  Files            26       26              
  Lines           689      691       +2     
  Branches         71       73       +2     
============================================
+ Hits            557      559       +2     
  Misses           92       92              
  Partials         40       40              

Impacted Files	Coverage Δ
ballerina/client.bal	100.00% <0.00%> (ø)
ballerina/listener.bal	100.00% <0.00%> (ø)

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