vcpkg: use x-azcopy as x-azblob requires SAS token (even in read scenarios) (Azure#3076)

vcpkg introduced a new set of features and changed behavior for
`x-azblob` in cases where no SAS is provided. There's an `x-azcopy`
configuration which does not require SAS and works in `read` scenarios.

Successful PR build:
https://dev.azure.com/azure-sdk/public/_build/results?buildId=5404051&view=logs&j=f62abde3-0c2c-58c2-34fa-f25f24e797de&t=7bf7baf7-4679-52b3-46c9-d10933f9b078
Successful internal build:
https://dev.azure.com/azure-sdk/internal/_build/results?buildId=5404053&view=logs&j=f62abde3-0c2c-58c2-34fa-f25f24e797de&t=7bf7baf7-4679-52b3-46c9-d10933f9b078

Author: danieljurek

eng/pipelines/templates/steps/vcpkg.yml

@@ -1,6 +1,6 @@
 steps:
   - pwsh: |
-      Write-Host '##vso[task.setvariable variable=VCPKG_BINARY_SOURCES_SECRET;issecret=true;]clear;x-azblob,https://azuresdkartifacts.blob.core.windows.net/public-vcpkg-container,,read'
+      Write-Host '##vso[task.setvariable variable=VCPKG_BINARY_SOURCES_SECRET;issecret=true;]clear;x-azcopy,https://azuresdkartifacts.blob.core.windows.net/public-vcpkg-container,read'
       Write-Host '##vso[task.setvariable variable=X_VCPKG_ASSET_SOURCES_SECRET;issecret=true;]clear;x-azurl,https://azuresdkartifacts.blob.core.windows.net/public-vcpkg-container,,read'
     displayName: Set vcpkg variables
 

eng/scripts/Set-VcpkgWriteModeCache.ps1

@@ -42,5 +42,5 @@ Write-Host "Ensure redaction of SAS tokens in logs"
 Write-Host "##vso[task.setvariable variable=VCPKG_BINARY_SAS_TOKEN;issecret=true;]$vcpkgBinarySourceSas"
 
 Write-Host "Setting vcpkg binary cache to read and write"
-Write-Host "##vso[task.setvariable variable=VCPKG_BINARY_SOURCES_SECRET;issecret=true;]clear;x-azblob,https://$StorageAccountName.blob.core.windows.net/$StorageContainerName,$vcpkgBinarySourceSas,readwrite"
+Write-Host "##vso[task.setvariable variable=VCPKG_BINARY_SOURCES_SECRET;issecret=true;]clear;x-azcopy-sas,https://$StorageAccountName.blob.core.windows.net/$StorageContainerName,$vcpkgBinarySourceSas,readwrite"
 Write-Host "##vso[task.setvariable variable=X_VCPKG_ASSET_SOURCES_SECRET;issecret=true;]clear;x-azurl,https://$StorageAccountName.blob.core.windows.net/$StorageContainerName,$vcpkgBinarySourceSas,readwrite"