Add <Input> type variants url, email, and number

[yhatt]

Extend type prop variants for <Input> component, to support URL input, email input, and number input. Slack app can provide proper input elements for purpose.

<Modal title="Input variants">
  <Input type="text" label="Text" />
  <Input type="url" label="URL" />
  <Input type="email" label="Email" />
  <Input type="number" label="Number" min={0} max={1000} />
</Modal>

This interface is very similar to jsx-slack v0's (outdated) dialog support.
https://github.com/yhatt/jsx-slack/blob/v0.11.0/docs/jsx-components-for-dialog.md#html5-types

Close #277.

ToDo

• Add <Input> type variants url, email, and number
• Update schema for demo
• Tests
• Documentations