Add Notification of the Removal of Gallery (#22341)

Author: msJinLei

src/Accounts/Accounts/help/Add-AzEnvironment.md

@@ -495,6 +495,7 @@ Accept wildcard characters: False
 
 ### -GalleryEndpoint
 Specifies the endpoint for the Azure Resource Manager gallery of deployment templates.
+The parameter is to set the value to `GalleryUrl` of `PSAzureEnvironment`. As `GalleryUrl` is removed from ArmMetadata, Azure PowerShell will no longer provide for the value and so it is not recommended to set `GalleryEndpoint` anymore.
 
 ```yaml
 Type: System.String

src/Accounts/Accounts/help/Get-AzEnvironment.md

@@ -9,6 +9,7 @@ schema: 2.0.0
 
 ## SYNOPSIS
 Get endpoints and metadata for an instance of Azure services.
+`GalleryUrl` will be removed from ArmMetadata and so Azure PowerShell will no longer provide for its value in `PSAzureEnvironment`. Currently `GalleryUrl` is not used in Azure PowerShell products. Please do not reply on `GalleryUrl` anymore. 
 
 ## SYNTAX
 

src/Accounts/Accounts/help/Set-AzEnvironment.md

@@ -417,6 +417,7 @@ Accept wildcard characters: False
 
 ### -GalleryEndpoint
 Specifies the endpoint for the Azure Resource Manager gallery of deployment templates.
+The parameter is to set the value to `GalleryUrl` of `PSAzureEnvironment`. As `GalleryUrl` is removed from ArmMetadata, Azure PowerShell will no longer provide for the value and so it is not recommended to set `GalleryEndpoint` anymore.
 
 ```yaml
 Type: System.String