Relax converter within keymap schema (#19544)

data/schemas/keymap.jsonschema

@@ -7,7 +7,8 @@
         "author": {"type": "string"},
         "converter": {
             "type": "string",
-            "enum": ["elite_pi", "proton_c", "kb2040", "promicro_rp2040", "blok", "bit_c_pro", "stemcell", "bonsai_c4"]
+            "minLength": 1,
+            "pattern": "^[a-z][0-9a-z_]*$"
         },
         "host_language": {"$ref": "qmk.definitions.v1#/text_identifier"},
         "keyboard": {"$ref": "qmk.definitions.v1#/text_identifier"},