feat: add case:<id> and reply:<id> to sub claim

since we expand the API to handle replies, we need the reply in the sub
claim. additionally, if we want to move away from using the 'txn' claim
and use the 'sub' claim for cases, it must be possible to specify them
in the sub claim. thats why case:<id> was added.

spec/set-payload.schema.json

@@ -25,9 +25,9 @@
       "minimum": 1577833200
     },
     "sub": {
-      "description": "Das Subject ('sub') enthält 'submission:' und die UUID der Submission.",
+      "description": "Beschreibt, wen das SET betrifft.",
       "type": "string",
-      "pattern": "^submission:[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$"
+      "pattern": "^(case|submission|reply):[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$"
     },
     "txn": {
       "description": "Der Transaction Identifier ('txn') enthält 'case:' und die UUID des Cases.",