feat(invidious-companion): use connection pool

From
https://github.com/iv-org/invidious/pull/4985#discussion_r1889356705

Thanks syeopite!

src/invidious.cr

@@ -114,6 +114,10 @@ YT_POOL = YoutubeConnectionPool.new(YT_URL, capacity: CONFIG.pool_size)
 
 GGPHT_POOL = YoutubeConnectionPool.new(URI.parse("https://yt3.ggpht.com"), capacity: CONFIG.pool_size)
 
+COMPANION_POOL = CompanionConnectionPool.new(
+  capacity: CONFIG.pool_size
+)
+
 # CLI
 Kemal.config.extra_options do |parser|
   parser.banner = "Usage: invidious [arguments]"