[release/8.0] Generate and store random RG name when provisioning

[github-actions]

Backport of #3375 to release/8.0

/cc @davidfowl @sebastienros

Customer Impact

Deployments are using the machine name in the resource group name. This change uses a random number and stores the created resource group name in user secrets.

Testing

Manual validation of:

• New deployments use the random values
• New deployments can use the custom RG name and won't have any random value
• New deployments can use a custom RG prefix and a random value
• New deployments with random values are stored in user secrets
• Existing resource group name is reused from user secrets

Risk

Low. Users can also still force a custom resource group name.

Regression?

No.

Microsoft Reviewers: Open in CodeFlow