Add edit_url and layers_url attribute into initial client API response (ref: group-project-map-config)

[Raruto]

Motivation

1. See: Link to the edit project page g3w-client#391

2. improve #503 without requiring client to perform a subsequent to another API endpoint to get the edit_url of current project (ie: throught about-project-by-group-api-list you can actually gets the edit_url of all projects within the same group, somewhat resource expensive.. ⌛)

Sample Response

// GET http://localhost:8000/api/config/2/qdjango/3?_t=1703148279.973667

{
  "id": 3,
  "name": "Public building management Demo",
  "layerstree": [ ... ],
  "thumbnail": null,
  "wms_use_layer_ids": true,
  "qgis_version": "3.28.4-Firenze",
  "toc_layers_init_status": "not_collapsed",
  "toc_themes_init_status": "collapsed",
  "wms_getmap_format": "image/png; mode=8bit",
  "initextent": [...],
  "extent": [...],
  "print": [...],
  "layers": [...],
  "search": [],
  "widget": [],
  "relations": [...],
  "initbaselayer": null,
  "metadata": {...},
  "context_base_legend": true,
  "feature_count": 5,
  "querymultilayers": [...],
  "autozoom_query": false,
  "toc_tab_default": "layers",
  "legend_position": "tab",
  "ows_method": "GET",
  "html_page_title": "g3w - client | Public building management Demo",
  "search_endpoint": "ows",
  "bookmarks": [...],
  "map_themes": [...],
  "messages": {...},
  "edit_url": "/en/admin/qdjango/3857/projects/update/public-building-management-demo/" // <-- ADDED
  "layers_url": "/en/admin/qdjango/3857/projects/public-building-management-demo/layers/" // <-- ADDED
}

Related to: g3w-suite/g3w-client#392

[Raruto]

@wlorenzetti @volterra79 if you have better property names, just say...