Deprecate AzureRM - PowerShellContext

[rain-on]

The AzureRM deprecation flag is required to be included in the AzurePowershellContext.ps1 to show a warning if users are still using AzureRM module (Rather than Azure CLI).

This feature flag means users are presented with a warning atm - which will become an error at some point in the future.

The script update matches that performed in the prior AzureContext.ps1

Catches a piece missed in https://github.com/OctopusDeploy/Calamari/pull/1257

[sc-74652]