Add dimmable flag where known

L0001 (Philips LEDBulb) and L0002/L0003 (LAMPTAN Gloss V2) are
documented non-dimmable; L0012 is a halogen and inherently dimmable.
Others stay unknown until checked against their packaging.

lamps/L0012/metrics.json

@@ -2,6 +2,7 @@
   "name": "L0012",
   "ean": "4008321211828",
   "type": "halogen",
+  "dimmable": true,
   "rated": {
     "Power_W": 28,
     "lifetime_h": 2000,