[JENKINS-71737] rename cloudName to name

[car-roll]

Warning

This is a breaking change for anyone configuring Azure VM Agents with the configuration as code plugin

cloudName has been renamed to name adapt your templates

- cloudName: "linux"
+ name: "linux" 

Preparing for jenkinsci/jenkins#8310 where cloud name changes will be done on a separate page

The use of the variable name cloudName in AmazonEC2Cloud forces jenkins core to have a special case of handling cloudName when it not a variable of Cloud.
https://github.com/jenkinsci/jenkins/blob/d41b0f5807923286ad33d4847af95e2c6c7c77ba/core/src/main/java/jenkins/agents/CloudSet.java#L229

upstream of #460

Testing done

manually created, renamed, and deleted an AzureVMAgentsCloud

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[timja]

Tested locally, all seems fine