[EAK-654] Improve config change event handling

[smiakchilo]

Fixes #654

[Copilot]

Pull request overview

This PR addresses Issue #654 by making ConfigChangeListener more resilient to transient “missing resource” situations in clustered AEMaaCS author environments, reducing the risk of incorrectly treating a changed config as removed.

Changes:

• Added configurable “resolve-with-retry” behavior for resolving changed resources before deciding to reset configuration.
• Refactored async processing to use scheduled executors and improved shutdown handling.
• Expanded and refactored unit tests (moving away from Mockito in several cases) and added coverage for additional reset/update scenarios.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
core/src/main/java/com/exadel/aem/toolkit/core/configurator/services/ConfigChangeListener.java	Adds resolve-with-retry and reorganizes async execution/shutdown behavior for change processing.
core/src/main/java/com/exadel/aem/toolkit/core/configurator/services/ConfigChangeListenerConfiguration.java	Introduces OSGi config knobs for retry count and delay.
core/src/test/java/com/exadel/aem/toolkit/core/configurator/services/ConfigChangeListenerTest.java	Updates tests to use stubs and adds scenarios around update/reset behavior.

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