[Feature]: Add Flex Consumption app support to Update-AzFunctionApp

### Description of the new feature

**Description:**
Update-AzFunctionApp currently only supports Consumption v1, Dedicated, and Premium function apps. Add support for updating Flex Consumption apps, including:

- AlwaysReady configuration (array of trigger/instance-count pairs)
- MaximumInstanceCount, InstanceMemoryMB, HttpPerInstanceConcurrency
- Deployment storage settings (name, container, auth type/value)

Consider parity with Az CLI commands (az functionapp update, az functionapp scale config set, etc.) or introducing new cmdlets like:

-
- Set-AzFunctionAppScaleConfig - for scale and concurrency settings
- Set-AzFunctionAppDeploymentStorage - for deployment storage configuration

### Proposed implementation details (optional)

_No response_