Remove obsolete issue templates (04_core_feature_request, 05_mqissue), renumber 06_learn_feedback → 04 (Azure#58321)

* Initial plan

* Remove 04_core_feature_request and 05_mqissue templates, rename 06_learn_feedback to 04_learn_feedback

Agent-Logs-Url: https://github.com/Azure/azure-sdk-for-net/sessions/18b9e593-3291-47f1-aed8-ffddfe3ad096

Co-authored-by: jsquire <913445+jsquire@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jsquire <913445+jsquire@users.noreply.github.com>

Author: Copilot