Add an '-Identities <string[]:identities>' flag or similar to New-AzWebApp, New-AzWebAppSlot, Set-AzWebApp, and Set-AzWebAppSlot to support managing user-assigned managed identities on web apps and their slots. Also, consider deprecating/removing the non-functional -CopyIdentity from New-AzWebAppSlot.
### Description of the new feature Please add an `-Identities <string[]:identities>` flag or similar to `New-AzWebApp`, `New-AzWebAppSlot`, `Set-AzWebApp`, and `Set-AzWebAppSlot` to support managing user-assigned managed identities on web apps and their slots. Consider deprecating/removing `-CopyIdentity` from `New-AzWebAppSlot` which doesn't work. The ability to manage user assigned managed identities has existed for a while now in `az` CLI ([see here](https://learn.microsoft.com/en-us/cli/azure/webapp/identity?view=azure-cli-latest)) and it makes sense that Powershell should support it as well. Thanks! ### Proposed implementation details (optional) Presumably, implementation will be similar to what `az` CLI is using to assign them.