Support overriding Publish manifest for Visual Studio extensions

[jessehouwing]

Like the Azure DevOps extensions I'd love to add support for overriding:

  "priceCategory": "free",
  "publisher": "onlyutkarsh",
  "private": false,

Prior to publish.

@onlyutkarsh

[jessehouwing]

Looks like the version isn't part of the publish manifest, but of the source manifest. does it make sense to allow overriding that with the Azure DevOps build number somehow as well?