Custom Tools / SDK: Allow specifying an example workflow for any custom tools

[mkhtran]

All built-in Designer tools have an associated example workflow that can be opened by right-clicking a tool and selecting Open Example. This feature is invaluable in helping users familiarize themselves with a tool and explore all of its features. Custom tools should be able to specify example workflows of their own.

It is currently possible to specify an example workflow, but

1. The workflow must be specified by modifying a tool's `Config.xml` file, where changes may be overwritten by the SDK.
2. All paths are relative to `[AlteryxInstallDirectory]\Samples\[locale]\02 Learn_one_tool_at_a_time`, and there is no easy way to install workflows into this directory.

Specifying an example workflow

Developers should have a way to specify the example workflow associated with any custom tool. This would likely be done in the `ayx_workspace.json` file.

{
  "tools": {
    "MyCustomTool": {
      "configuration": {
        "example_path": "configuration\\MyCustomTool_1_0\\example.yxmd"
      }
    }
  }
}

Note that a workflow may depend on some external files as well. It would be ideal if an `assets_path` could be defined to easily allow any arbitrary assets to be included with your tool. (This is currently possible, but must be done by manually modifying the .yxi archive; it isn't handled by the SDK). This would easily allow for example workflows to be specified as a path relative to `assets_path`, and if the workflow contains any relative paths to files within the assets folder, they can be resolved.

{
  "tools": {
    "MyCustomTool": {
      "configuration": {
        "assets_path": "configuration\\MyCustomTool_1_0\\assets",
        "example_path": "example\\example.yxmd"
      }
    }
  }
}

Localization of the example workflow would also be supported when localization of the plugin configuration is supported.