FabricBot: Onboarding to GitOps.ResourceManagement because of FabricBot decommissioning (#8869)

* Add prIssueManagement.yml to onboard repo to GitOps.ResourceManagement as FabricBot replacement

 Details on the replacement service and the syntax of the new yaml configuration file is available publicly at: https://microsoft.github.io/GitOps/policies/resource-management.html

Please review and merge this PR to complete the process of onboarding to the new service.

* Deleting fabricbot.json

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Co-authored-by: dotnet-policy-service[bot] <123482357+dotnet-policy-service[bot]@users.noreply.github.com>

Author: dotnet-policy-service[bot]