Update .backportrc.json (#123)

Update the `.backportrc.json` so we can backport to `0.2`

.backportrc.json

@@ -1,12 +1,13 @@
 {
   "targetBranchChoices": [
     { "name": "main", "checked": true },
+    "0.2",
     "0.1"
   ],
   "fork": false,
   "targetPRLabels": ["backport"],
   "branchLabelMapping": {
-    "^v0.2.0(.0)?$": "main",
+    "^v0.3.0(.0)?$": "main",
     "^v(\\d+).(\\d+)(.\\d+)+$": "$1.$2"
   },
   "upstream": "elastic/crawler"