[Notification Template API] Add notification template management functions

[RushanNanayakkara]

Purpose

Updates NotificationTemplateManager to implement required functions for Notification Template API which supports template operations for all available notification channels. (Email, SMS)

Related Issues

• https://github.com/wso2-enterprise/asgardeo-product/issues/25122

Related PRs

• [Notification Template API] API Implementation wso2/identity-api-server#629
• [Notification Template API] Event Handler Implementation identity-event-handler-notification#250
• [Notification Template API] Add Notification Template API Resource wso2/carbon-identity-framework#5784

[jenkins-is-staging]

PR builder started
Link: https://github.com/wso2/product-is/actions/runs/9870606603

[jenkins-is-staging]

PR builder completed
Link: https://github.com/wso2/product-is/actions/runs/9870606603
Status: success

[jenkins-is-staging]

Approving the pull request based on the successful pr build https://github.com/wso2/product-is/actions/runs/9870606603

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.

Project coverage is 22.13%. Comparing base (a4ed43e) to head (d08b1e5).
Report is 59 commits behind head on master.

Files with missing lines	Patch %	Lines
...vice/notification/NotificationTemplateManager.java	0.00%	15 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #832      +/-   ##
============================================
- Coverage     22.15%   22.13%   -0.03%     
  Complexity      915      915              
============================================
  Files           267      267              
  Lines         15472    15486      +14     
  Branches       2092     2092              
============================================
  Hits           3428     3428              
- Misses        11590    11604      +14     
  Partials        454      454              

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