Extract New-ResourceGroup private command for reuse

[flanakin]

🛠️ Description

Extract the new RG creation from Deploy-FinOpsHub to reuse in other commands.

📋 Checklist

🔬 How did you test this change?

• 🤏 Lint tests
• 🤞 PS -WhatIf / az validate
• 👍 Manually deployed + verified
• 💪 Unit tests
• 🙌 Integration tests

🙋‍♀️ Do any of the following that apply?

• 🚨 This is a breaking change.
• 🤏 The change is less than 20 lines of code.

📑 Did you update docs/changelog.md?

• ✅ Yes (required for dev PRs)
• ➡️ Will cover in a future PR (feature branch PRs only)
• ❎ Not needed (small/internal change)

📖 Did you update documentation?

• ✅ Public docs in docs (required for dev)
• ✅ Internal dev docs in src (required for dev)
• ➡️ Will cover in a future PR (feature branch PRs only)
• ❎ Not needed (small/internal change)

[flanakin]

Suggested change

	.EXAMPLE
	New-ResourceGroup -WhatIf
	Shows what would happen if the command runs without actually running it.
	.DESCRIPTION
	The New-ResourceGroup command performs any initialization tasks required for a resource group contributor to be able to deploy a FinOps hub instance in Azure, like registering resource providers. To view the full list of tasks performed, run the command with the -WhatIf option.
	.DESCRIPTION
	The New-ResourceGroup command performs any initialization tasks required for a resource group contributor to be able to deploy a FinOps hub instance in Azure, like registering resource providers. To view the full list of tasks performed, run the command with the -WhatIf option.
	.EXAMPLE
	New-ResourceGroup -WhatIf
	Shows what would happen if the command runs without actually running it.

[flanakin]

Add parameters to the docs