Editor defaultvalue from json property in session or local storage

[MattiasSp]

Fixes #2218.

Adds the possibility to extract a subvalue from a returned JSON object when getting editor default values from sessionStorage or localStorage.

Now, by specifying the parameter "keyType": "json_path" and using simple dot-notation in the key parameter, values can be extracted from anywhere within the response, provided it can be parsed as JSON. It also works with array indices (e g sessionStorageVariable[2].object.array[0].value).

Config example:

"attributes": [
  {
    "name": "skapad_av",
    "title": "Skapad av: ",
    "type": "hidden",
    "defaultValue": {
      "type": "sessionStorage",
      "keyType": "json_path",
      "key": "oidc_user.displayname",
      "updateOnEdit": false
    }
  }
]

[steff-o]

LGTM!

If the json path is not a leaf, it will get "[Object object]" as default. All other errors will just be empty string. Probably not an issue as it is only the result of bad configuration.