Add Original Image Url to the API

[ismailsunni]

Currently, the API only gives the thumbnail URL. It's enough for some cases, but for other cases the good bigger image is better.

Example:
{
            "resource_type": "Geopackage",
            "resource_subtype": null,
            "uuid": "4bd7fb37-3743-4c13-9c06-713d334d1632",
            "name": "QGIS Dashboard",
            "creator": "Tim Sutton",
            "upload_date": "2020-12-14T03:27:07.065270",
            "download_count": 2889,
            "description": "This is a demonstrator project to show how you might use labels to create a dashboard in QGIS. The project requires that you have the UN-OCHA Free Font installed. You can find the font for free here:\r\n\r\n[Humanitarian-Font](https://unhcr.github.io/Humanitarian-Font/)\r\n\r\nIf you make a selection of roads or buildings, the dashboard will update automatically to show the selection count.\r\n\r\nLikewise, adding a new flood polygon or altering the existing flood polygon will update the flooded building and roads counts.\r\n\r\nThis is a demonstrator project - it may not be practical for large datasets or indeed for anything in an of itself. It is intended to show you some techniques for working with data driven labels and aggregate expressions as well as perhaps inspiring you to do interesting things with QGIS in your own work.\r\n\r\nYou can find a detailed interactive walk through of the techniques used to make this dashboard in this video: [[https://youtu.be/lJTV90SvRAM](https://youtu.be/lJTV90SvRAM)\r\n\r\nThe](https://youtu.be/lJTV90SvRAM](https://youtu.be/lJTV90SvRAM)%5Cr%5Cn%5Cr%5CnThe) building and roads layers is courtesy of the OpenStreetMap project. OpenStreetMap® is open data, licensed under the Open Data Commons Open Database License (ODbL) by the OpenStreetMap Foundation (OSMF). You can find out more at [openstreetmap](http://openstreetmap.org)",
            "file": "https://plugins.qgis.org/media/geopackages/2020/CasteloBrancoDashboardAnchored_X3UlC1k.zip",
            "thumbnail": "https://plugins.qgis.org/media/cache/fc/34/fc347c5a699829b2a7b31d7a7bf8dd26.jpg"
        },

[dimasciput]

@ismailsunni you can access the full thumbnail image now with thumbnail_full in the new api.