x-prompt should support an array of defaults for lists

[d-koppenhagen]

🚀 Feature request

Command (mark with an x)

- [x] new
- [ ] build
- [ ] serve
- [ ] test
- [ ] e2e
- [x] generate
- [x] add
- [x] update
- [ ] lint
- [ ] xi18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc

Description

A clear and concise description of the problem or missing capability...

Within angular-cli 9.0.0-rc.0 it's possible to create schematics that will allow to use x-prompts with multi selection like this way:

{
  "$schema": "http://json-schema.org/schema",
  "id": "ngx-semantic-version",
  "title": "ngx-semantic-version Schema",
  "description": "configure commitlint, husky, commitizen and standard-version configuration",
  "type": "object",
  "properties": {
    "packages": {
      "type": "array",
      "description": "select the packages that should to be installed and configured",
      "uniqueItems": true,
      "items": {
        "type": "string"
      },
      "x-prompt": {
        "message": "What packages do you want to be installed and configured?",
        "type": "list",
        "multiselect": true,
        "items": ["commitlint", "commitizen", "husky", "standard-version"]
      }
    },
  },
  "required": ["packages"]
}

As the result of the x-prompt will lead into an array of values instead of a single selected value or input, it should be also supported to configure and array of default values.

Describe the solution you'd like

It should be possible to configure "default": ["foo", "bar"], inside the properties:

{
  "$schema": "http://json-schema.org/schema",
  "id": "ngx-semantic-version",
  "title": "ngx-semantic-version Schema",
  "description": "configure commitlint, husky, commitizen and standard-version configuration",
  "type": "object",
  "properties": {
    "packages": {
      "type": "array",
      "description": "select the packages that should to be installed and configured",
      "uniqueItems": true,
      "items": {
        "type": "string"
      },
      "default": ["commitlint", "commitizen", "husky", "standard-version"],
      "x-prompt": {
        "message": "What packages do you want to be installed and configured?",
        "type": "list",
        "multiselect": true,
        "items": ["commitlint", "commitizen", "husky", "standard-version"]
      }
    },
  },
  "required": ["packages"]
}

Describe alternatives you've considered

Have you considered any alternative solutions or workarounds?