rpo: try 'required: true' to force-enable CC ReCreated, 0.21.2 -> 0.21.3

Players with an existing options.txt (i.e. anyone who has launched MC
once) don't get the 'default_packs' applied -- RPO only treats those as
defaults for fresh installs.

Adding 'required: true' to the override entry on the assumption that
the field forces the pack to be enabled on every launch regardless of
player choice. Decompiled the jar for string constants and 'required'
appears alongside 'force_compatible' as a known key.

If the field name is wrong RPO will silently ignore it -- no harm, easy
iteration.

pack/pack.lock.json

@@ -1,7 +1,7 @@
 {
   "$schema": "Brass-and-Sigil pack.lock.json - generated, do not edit by hand unless you know what you are doing",
   "name": "Brass and Sigil",
-  "version": "0.21.2",
+  "version": "0.21.3",
   "minecraft": "1.21.1",
   "loader": {
     "type": "neoforge",