[Documentation] Update FinOps hub cost estimation

🐛 Problem

Cost is much higher than indicated in documentation.
In our case, core issue are higher cost in West Europe, but I think costs also increased in time.

Link:
https://learn.microsoft.com/en-us/cloud-computing/finops/toolkit/hubs/finops-hubs-overview

In Our case just ADX costs would be over 220 EUR/month with basic setup ...
First issue is ADX region pricing as there are lots of regional differences WestEU comparing to other locations.
Also there seems to be other ADX cost that are not part of the estimation, ... Storage, load balancer, PIP, ...

I cannot do proper cost estimation, I our case I switched ADX SKU to more modern and cheaper E2a_v4 SKU and implemented start/stop solution so the ADX is running only 12h daily on work days.

🤔 Expected

This is my suggestion, but this is just idea, to make more clear how the expected costs will be ...

Estimated cost: Starts at $160/mo + $10/mo per $1M in cost being monitored for deployment with ADX.

Estimated monthly cost depends on FinOps HUB deployment:

1.) Storage only: Azure Data Factory +  storage accounts < 10$/mo
2.) Azure Data Explorer (ADX): ADX DevSKU 150$ + (Azure Data Factory +  storage accounts) 10$ = 160$/mo
3.) Azure Fabric: $300 for F2 Fabric capacity + (Azure Data Factory +  storage accounts) 10$  = 310$/mo

Exact cost will vary based on type of FinOps Hub deployed, discounts, region, data size (we estimate ~20GB per $1M), and Fabric or Power BI license requirements.
Storage only Hub cost is 5-10$ per $1M in cost being monitored. For details, refer to the FinOps hub cost estimate in the Azure Pricing Calculator.

Start with the FinOps Hubs overview page linked in the issue and compare its published estimates with the Azure Pricing Calculator. Check the Storage-only, ADX, and Fabric scenarios, including regional pricing and the additional services named in the issue. Done means the documentation clearly states updated estimates, assumptions, regional variation, and what costs are excluded.