feat(metabranch): add batch actions support

[antongolub]

{
  "plugins": [[
    "@qiwi/semrel-multibranch",
    {
      "verify": [{
        "action": "fetch",
        "branch": "metabranch",
        "from": "foo",
        "to": "bar"
      }, {
        "action": "fetch",
        "branch": "changelog",
        "from": "./CHANGELOG.md",
        "to": "."
      }],
     "publish": {
        "action": "push",
        "branch": "changelog",
        "from": "./CHANGELOG.md",
        "to": "."
      }
    }
  ]]
}