[Issue] Fix for communication.xml Handlers merging processs

[m2-assistant]

This issue is automatically created based on existing pull request: #28926: Fix for communication.xml Handlers merging processs

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Description (*)

This changes fixes the "handler" merging process into communication.xml files which currently overrides all the handlers with the last one created, ignoring it's different names as expected. Issue found during custom handler development for MCOM module where there was already a handler for a message.

Manual testing scenarios (*)

1. Develop a module which defines two handlers, with different names, for a same request on communication.xml
2. Check config after flush cache, it will only includes the last handler specified.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)