auto_profiles.lua: make profiles apply with higher priority

This increases the priority from 50 (which is neutral) to ensure that
profiles are applied before other scripts.

In general, applying profiles before other scripts makes sense. This was
already the case for external scripts with default priority because they
would load after auto_profiles.

This commit primarily fixes ytdl_hook.lua to respond to profile changes.
In most cases, profile conditions are triggered by external conditions,
not the output from the ytdl hook, so this is fine.

I acknowledge that this will change the order if a script previously had
a priority lower than 50. However, injecting itself before profiles are
evaluated is a very obscure use case, if there is even a valid one.

DOCS/interface-changes/auto-profiles-prio.txt

@@ -0,0 +1 @@
+Change auto profiles hook priority from 50 to 5

player/lua/auto_profiles.lua

@@ -203,5 +203,5 @@ end)
 
 mp.register_idle(on_idle)
 for _, name in ipairs({"on_load", "on_preloaded", "on_before_start_file"}) do
-    mp.add_hook(name, 50, on_hook)
+    mp.add_hook(name, 5, on_hook)
 end