[2201.12.x] Add a notification to publish artifacts to the client

[nipunayf]

Purpose

The PR defines a new notification allowing the LS to send notifications to the client upon project updates. Additionally, this resolves concurrency issues in the event pub-sub handler.

Fixes wso2/product-ballerina-integrator#88

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 77.29%. Comparing base (3417667) to head (c48773a).
Report is 12 commits behind head on 2201.12.x.

Files with missing lines	Patch %	Lines
...ng/langserver/eventsync/EventSyncPubSubHolder.java	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##             2201.12.x   #43963      +/-   ##
===============================================
- Coverage        77.29%   77.29%   -0.01%     
- Complexity       59094    59106      +12     
===============================================
  Files             3540     3540              
  Lines           222378   222410      +32     
  Branches         28837    28843       +6     
===============================================
+ Hits            171892   171914      +22     
- Misses           40778    40786       +8     
- Partials          9708     9710       +2     

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