Add error message when deploying to flex apps with python 3.14

[gavin-aguiar]

This PR adds validation to prevent deploying Python 3.14 function apps to Flex Consumption plans, as remote build is not currently supported for this configuration.

Changes

• Added a check in the deployment flow to detect when a Python 3.14 app is being deployed to a Flex Consumption function app
• The validation reads the functionAppConfig.runtime.version property from the remote site configuration
• When Python 3.14 on Flex is detected, the deployment is blocked with a clear error message
• The error message includes a reference link (https://aka.ms/py314-remote-build-flex) for more information