Changes to allow reporting success with an action on sqlTasksService

[allancascante]

Description

This PR refactors the task completion notification system to eliminate duplicate notifications for DacFx operations (Export BACPAC, Extract DACPAC, Import BACPAC, Deploy DACPAC) and provides a generic, configurable solution for custom task completion handlers, as reported in this bug.

Problem
Previously, DacFx operations showed two notifications:

A custom notification with action button from dacpacDialogWebviewController
A generic completion notification from sqlTasksService

Solution

Centralized all task completion notification logic in sqlTasksService with a configurable handler registration system.

Code Changes Checklist

• New or updated unit tests added
• All existing tests pass (npm run test)
• Code follows contributing guidelines
• Telemetry/logging updated if relevant
• No regressions or UX breakage

Reviewers: Please read our reviewer guidelines

[github-actions]

PR Changes

Category	Target Branch	PR Branch	Difference
vscode-mssql VSIX	5289 KB	5289 KB	⚪ 0 KB ( 0% )
sql-database-projects VSIX	5668 KB	5668 KB	⚪ 0 KB ( 0% )
data-workspace VSIX	null KB	542 KB	⚪ 542 KB ( 0% )

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.61111% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 66.60%. Comparing base (24d2641) to head (da1764e).

Files with missing lines	Patch %	Lines
extensions/mssql/src/controllers/mainController.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20651      +/-   ##
==========================================
+ Coverage   66.33%   66.60%   +0.27%     
==========================================
  Files         210      210              
  Lines       20235    20272      +37     
  Branches     2634     2638       +4     
==========================================
+ Hits        13423    13503      +80     
+ Misses       6716     6671      -45     
- Partials       96       98       +2     

Files with missing lines	Coverage Δ
extensions/mssql/src/constants/constants.ts	100.00% <100.00%> (ø)
...l/src/controllers/dacpacDialogWebviewController.ts	92.16% <ø> (+0.64%)	⬆️
extensions/mssql/src/services/dacFxService.ts	51.38% <100.00%> (+46.12%)	⬆️
extensions/mssql/src/services/sqlTasksService.ts	85.04% <100.00%> (+48.57%)	⬆️
extensions/mssql/src/controllers/mainController.ts	17.27% <0.00%> (ø)

... and 3 files with indirect coverage changes

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