azure-pipelines: Extension release template improvements

[alexweininger]

The focus of these improvements is to add safety features to prevent mistakes and accidental releases. These include:

1. Releases will require approval from an environment. The environment can be specified and every environment can have a different group of approvals. And you can enable/disable self approval.
2. A version string is required at pipeline run time that will be matched against the version present in the package.json downloaded from the build pipeline artifacts.
3. Added a "Dry Run" parameter that when set will skip the last step that actually publishes the extension.