Add VS Code Extension

Is your feature request related to a problem? Please describe.
I would like to have my VS code extensions installed when I receive my Dev Box

Describe the solution you'd like
As a user, I should be able to:

1. specify a list of extensions (extension version optional) that ought to be installed on my Dev Box, using
2. extension id
3. path to file that contains export of code --list-extensions

setupTasks:

 - task: install-vscode-extension
    inputs:
      extension: "packageName@version "
      additionalOptions: 

For V1, we will NOT be supporting path to a JSON export of extensions from VS Code

 - task: install-vscode-extension
    inputs:
      extensions: "path/to/extension/list/export"
      additionalOptions: 

Start by locating the setupTasks task handlers and existing task definitions for the install-vscode-extension syntax. Implement extension installation by extension ID, with an optional version and support for a path to a code --list-extensions export; confirm that JSON exports are excluded from V1.