cat data/ann.json | jq " .metadata.annotations | to_entries | map(select(.key | test("label[1-9]"))) " 
[
  {
    "key": "label1",
    "value": "stam"
  },
  {
    "key": "label2",
    "value": "another"
  },
  {
    "key": "label3",
    "value": "one"
  }
]