Feature: Add resource type URL to writeFiles step

[bph]

During the update of the blueprints, I tried to use the step writeFiles like this (which didn't work)

"step": "writeFiles",
		"writeToPath": "/wordpress/wp-content",
		"filesTree": {
		  "resource": "literal:directory",
		  "name": "wp-content",
		  "files": {
			"postcontent.md": {
			  "resource": "url",
			  "url": "https://raw.githubusercontent.com/wordpress/blueprints/trunk/blueprints/wpcli-post-with-image/postcontent.md"
			},
			"Select-storage-method.png": {
			  "resource": "url",
			  "url": "https://raw.githubusercontent.com/wordpress/blueprints/trunk/blueprints/wpcli-post-with-image/Select-storage-method.png"
				}
			  }
			}

@bgrgicak took another look at this and found the following:

Your original Blueprint created a directory with the name postcontent.md and added files named resource and url to the directory.

This behavior matches our implementation of writeFile where a file can only be a literal value or another file tree (represented as a JSON object in the Blueprint).

"It would be mind blowing if we could append resource types like URLs in the way you attempted it, so it might be worth submitting a feature request to start a discussion." -- @bgrgicak

I strongly agree. It feels natural and allows for a more organized approach.

this is the current working implementation using writeFile step.

{
			"step": "writeFile",
			"path": "/wordpress/wp-content/postcontent.md",
			"data": {
				"resource": "url",
				"url": "https://raw.githubusercontent.com/wordpress/blueprints/trunk/blueprints/wpcli-post-with-image/postcontent.md"
			}
		},
		{
			"step": "writeFile",
			"path": "/wordpress/wp-content/Select-storage-method.png",
			"data": {
				"resource": "url",
				"url": "https://raw.githubusercontent.com/wordpress/blueprints/trunk/blueprints/wpcli-post-with-image/Select-storage-method.png"
			}
		},

It could look like this or something similar

{
"step": "writeFiles",
		"writeToPath": "/wordpress/wp-content",
		"filesTree": {
		  "resource": "literal:directory",
		  "name": "wp-content",
		  "files": {
			"postcontent": {
			        "resource": "url",
			         "postcontent.md": "https://github.com/WordPress/blueprints/blob/trunk/blueprints/wpcli-post-with-image/postcontent.md"
                                 },
			      { 
                               "resource": "url",
			        "Select-storage-method.png": "https://github.com/WordPress/blueprints/blob/trunk/blueprints/wpcli-post-with-image/Select-storage-method.png"}
			  }
	         }
	}
}

this would place the two files into the same directory

±---/wp-content
       |------/postcontent/
                     |-- postcontent.md
                     |--  Select-storage-method.png