feat: custom instructions in the checkbox type

[zonemeen]

It is now possible to customize the instructions in the checkbox type, for #1138

Instructions support for string or boolean type.

1.When instructions set to false, the help tip disappear:

{
      type: 'checkbox',
      message: 'Select a package manager',
      instructions: false,
      choices: [
          { name: 'npm', value: 'npm' },
          { name: 'yarn', value: 'yarn' },
          { name: 'jspm', value: 'jspm', disabled: true },
      ],
}

2.When instructions set to string, the help tip is customized:

{
      type: 'checkbox',
      message: 'Select a package manager',
      instructions: '空格单选，a键全选，i键取消选择',
      choices: [
          { name: 'npm', value: 'npm' },
          { name: 'yarn', value: 'yarn' },
          { name: 'jspm', value: 'jspm', disabled: true },
      ],
}

3.When instructions are not set or set other values, the help tip is default:

{
      type: 'checkbox',
      message: 'Select a package manager',
      choices: [
          { name: 'npm', value: 'npm' },
          { name: 'yarn', value: 'yarn' },
          { name: 'jspm', value: 'jspm', disabled: true },
      ],
}

[SBoudrias]

Thanks!! It's been released as @inquirer/checkbox@0.0.22-alpha.0