feat: Add Video Cache compression

Video information from youtube always weight about ~60KB uncompressed.
When using Deflate to compress that information, it gets compressed down
to ~15KB, so now you will be able to store up to 4x entries more with
caching enabled.

For context, nadeko.net Invidious instance stores 54.7k keys, since we
also store the `time` in a different key associated to the video ID, the
real count of videos cached would be 27.3k. With compression enabled,
the Redis database will be able to store up to 4 times more videos in
cache, which is 109.2k videos cached.

Pretty cool huh.

src/invidious/config.cr

@@ -238,6 +238,8 @@ class Config
     property backend : Int32 = 1
     # Max quantity of keys that can be held on the LRU cache
     property lru_max_size : Int32 = 18432 # ~512MB
+    # Compress cache with Deflate
+    property compress : Bool = false
   end
 
   property check_backends_interval : Int32 = 30
@@ -453,6 +455,10 @@ class Config
         puts "1 (Redis compatible DB) (Default)"
         puts "2 (In memory LRU)"
       end
+      if config.video_cache.compress && config.video_cache.backend == 0
+        puts "Video Cache compression can only be enabled when using backend 1 (Redis) or 2 (LRU)"
+        exit(1)
+      end
     end
 
     # Check if the socket configuration is valid