[PowerShell][Hubs] Document Add-FinOpsServicePrincipal

[flanakin]

⚠️ Problem

Adding a service principal for EA accounts is difficult to manage via API.

🛠️ Solution

Validate and document the Add-FinOpsServicePrincipal command in PowerShell and hubs scope configuration docs.

🙋‍♀️ Ask for the community

We could use your help:

1. Please vote this issue up (👍) to prioritize it.
2. Leave comments to help us solidify the vision.

[bzlowrance]

(👍) Highly agree with this one, as this is a common scenario when deploying the FinOps dashboard which can lead to hours of time wasted for those who are not familiar with the REST API calls. The FinOps HUB has been rolled into the Azure Cost Optimization Assessment, one of our most popular MS deliveries affecting a large pool of CSA's who deliver it.