feat(dynamic_hook): support non request-scoped hooks

When a disabled and non-request scoped hook was called outside of
a request scope, it was producing an error while trying to index ngx.ctx

This commit adds a check to early return from is_group_enabled when
outside of the request scope

This allows for hooks to still work when used in other contexts where
they can be enabled via the always_enable() function

kong/dynamic_hook/init.lua

@@ -1,3 +1,5 @@
+local get_request = require "resty.core.base".get_request
+
 local ngx           = ngx
 local type          = type
 local pcall         = pcall
@@ -233,6 +235,10 @@ function _M.is_group_enabled(group_name)
     return true
   end
 
+  if not get_request() then
+    return false
+  end
+
   local dynamic_hook = ngx.ctx.dynamic_hook
   if not dynamic_hook then
     return false