[FEATURE] [SQL database] Add properties.backupRetentionDays setter for SQLDatabase items

Use Case / Problem

Fabric CLI can read (get) SQL database properties, but cannot update backup retention via CLI. Teams managing multiple environments (dev/test/prod) need to standardize and automate retention settings (e.g., 7/14/21/35 days) without manual portal steps.

Proposed Solution

Add support for setting properties.backupRetentionDays on *.SQLDatabase items using the existing set command pattern (property path via -q, input via -i).

Sample command:

• set <DBname>.SQLDatabase -q "properties.backupRetentionDays" -i 21

Expected behavior:

• Validate input is an integer and within the service-allowed range (fail with a clear error if not).
• Confirm the updated value in the command output (or return the updated resource payload).

Alternatives Considered

• Manually updating retention in the Fabric UI (not automatable and leads to configuration drift).

Impact Assessment

• This aligns with Microsoft Fabric roadmap items

Implementation Attestation

• I understand this feature should maintain backward compatibility with existing commands
• I confirm this feature request does not introduce performance regressions for existing workflows
• I acknowledge that new features must follow fabric-cli's established patterns and conventions

Implementation Notes

This should mirror existing property updates already supported by set for other item types.