fix(newrelic): set default revision template for notifications

[gerardvanengelen]

Custom Revision Template for NewRelic Service

Goal

Allow specifying a custom revision template for the NewRelic notification service, which enables support for projects with multiple sources. The default template assumes a specific structure ({{.app.status.operationState.syncResult.revision}}) that doesn't work for all project configurations, especially those with multiple sources.

Changes Made

• Modified the NewrelicNotification.GetTemplater method to use the Revision field as a template string when provided by the user
• Maintained backward compatibility by keeping the default template when no custom revision is specified
• Aligned the implementation with the pattern used by other fields (Changelog and User) that already support custom templates

Tests Added

Updated TestGetTemplater_Newrelic in newrelic_test.go with two test cases:

1. "default revision template" - Tests the original behavior where the default template {{.app.status.operationState.syncResult.revision}} is used when no custom Revision is provided
2. "custom revision template" - Tests the new functionality where a custom template specified in the Revision field ({{.app.status.custom.revision}}) is used instead of the default

These tests verify that users can now configure custom paths to retrieve revision information that matches their specific project structure, including support for multiple sources.

[GVengelen]

@pasha-codefresh Sorry to ping you directly, can you let me know if there are additional steps I need to take to get this reviewed?
This change would really help me, so it would be a shame if it is not reviewed because I miss something.