Add JSON Output Option and Refactor Data Preparation

[egze]

This pull request introduces a new -json flag, allowing output in JSON format for more flexible data handling and integration with other scripts. At the moment I'm trying to make enpass-cli work with Kamal basecamp/kamal#1189 (comment)

The change refactors the code by encapsulating card data preparation and output functionalities into reusable functions: prepareCardData and outputDataOrLog. The key points of this PR are:

Simple usage

> go run ./cmd/... -json -vault=path/to/vault list FooBar

Enter vault password:
[{"category":"computer","label":"DB_PASSWORD","login":"","title":"FooBar","type":"password"},{"category":"computer","label":"OTHER_SECRET","login":"","title":"FooBar","type":"password"},{"category":"computer","label":"","login":"","title":"FooBar","type":"password"},{"category":"computer","label":"","login":"","title":"FooBar","type":"password"}]

In combination with other scripts

> go run ./cmd/... -json -vault=path/to/vault list FooBar | jq

Enter vault password:
[
  {
    "category": "computer",
    "label": "DB_PASSWORD",
    "login": "",
    "title": "FooBar",
    "type": "password"
  },
  {
    "category": "computer",
    "label": "OTHER_SECRET",
    "login": "",
    "title": "FooBar",
    "type": "password"
  },
  {
    "category": "computer",
    "label": "",
    "login": "",
    "title": "FooBar",
    "type": "password"
  },
  {
    "category": "computer",
    "label": "",
    "login": "",
    "title": "FooBar",
    "type": "password"
  }
]

The same also works with show function.