fleet: add .net sdk config

[ryanzhang-oss]

Add the .net SDK auto-generation configuration for fleet

[github-actions]

Next Steps to Merge

Next steps that must be taken to merge this PR:

• ❌ This PR targets either the main branch of the public specs repo or the RPSaaSMaster branch of the private specs repo. These branches are not intended for iterative development. Therefore, you must acknowledge you understand that after this PR is merged, the APIs are considered shipped to Azure customers. Any further attempts at in-place modifications to the APIs will be subject to Azure's versioning and breaking change policies. Additionally, for control plane APIs, you must acknowledge that you are following all the best practices documented by ARM at aka.ms/armapibestpractices. If you do intend to release the APIs to your customers by merging this PR, add the PublishToCustomers label to your PR in acknowledgement of the above. Otherwise, retarget this PR onto a feature branch, i.e. with prefix release- (see aka.ms/azsdk/api-versions#release--branches).

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API Change Check

APIView identified API level changes in this PR and created the following API reviews

Language	API Review for Package
Go	sdk/resourcemanager/containerservicefleet/armcontainerservicefleet
JavaScript	@azure/arm-containerservicefleet
Python	azure-mgmt-containerservicefleet
Java	com.azure.resourcemanager:azure-resourcemanager-containerservicefleet