feature/boss-sprites-and-badges (#22)

Reviewed-on: TheFurya/nuzlocke-tracker#22
Co-authored-by: Julian Tabel <juliantabel.jt@gmail.com>
Co-committed-by: Julian Tabel <juliantabel.jt@gmail.com>

backend/src/app/seeds/data/firered-bosses.json

@@ -145,9 +145,9 @@
   {
     "name": "Giovanni",
     "boss_type": "gym_leader",
-    "specialty_type": null,
-    "badge_name": "50",
-    "badge_image_url": "/badges/50.png",
+    "specialty_type": "ground",
+    "badge_name": "Earth Badge",
+    "badge_image_url": "/badges/earth-badge.png",
     "level_cap": 50,
     "order": 8,
     "after_route_name": null,
@@ -167,7 +167,7 @@
     "after_route_name": null,
     "location": "Indigo Plateau",
     "section": null,
-    "sprite_url": null,
+    "sprite_url": "/boss-sprites/firered/lorelei.png",
     "pokemon": []
   },
   {
@@ -181,7 +181,7 @@
     "after_route_name": null,
     "location": "Indigo Plateau",
     "section": null,
-    "sprite_url": null,
+    "sprite_url": "/boss-sprites/firered/bruno.png",
     "pokemon": []
   },
   {
@@ -195,7 +195,7 @@
     "after_route_name": null,
     "location": "Indigo Plateau",
     "section": null,
-    "sprite_url": null,
+    "sprite_url": "/boss-sprites/firered/agatha.png",
     "pokemon": []
   },
   {
@@ -209,7 +209,7 @@
     "after_route_name": null,
     "location": "Indigo Plateau",
     "section": null,
-    "sprite_url": null,
+    "sprite_url": "/boss-sprites/firered/lance.png",
     "pokemon": []
   },
   {
@@ -223,7 +223,7 @@
     "after_route_name": null,
     "location": "Indigo Plateau",
     "section": null,
-    "sprite_url": null,
+    "sprite_url": "/boss-sprites/firered/blue.png",
     "pokemon": [
       {
         "pokeapi_id": 18,