Fix CPU metrics mixed for different Azure SQL databases on same server

[tnguyen7s]

Summary

• GetServerNameForStorage() used only the server hostname to generate storage keys, so multiple Azure SQL databases on the same logical server produced identical server_ids and their metrics were conflated
• Include DatabaseName in the storage key when set, following the existing pattern used for :RO (ReadOnlyIntent) connections

Fixes #677

Test plan

• Build compiles without warnings (there are 3 warnings, CS8602: Dereference of a possibly null reference, that appear to happen before the changes)
• Connect two Azure SQL databases on the same logical server with different database names
• Wait for initial collection (5 minutes)
• Verify FinOps > Utilization shows separate CPU stats (Average, P95, Maximum) for each database
• Code follows the style guidelines
• No hardcoded paths or credentials
• Changes are documented (comments, README if applicable)

[erikdarlingdata]

Great fix and thorough testing! We had independently landed on the same approach on our side (#679). One minor suggestion — would you mind switching the separator from : to / so the storage key reads server/database:RO instead of server:database:RO? Keeps the :RO suffix unambiguous. Either way, thanks for the contribution and the real-world Azure SQL DB validation!