Validate required fields and amount of requirements

:koala: :+1: 

This PR adds validation for required fields for requirements.
Plus, it validates if the amount of requirements is at most 10.

### RELATED

- [Translation PR](https://github.com/zendesk/zendesk_apps_support/pull/61)

### REFERENCE

- [JIRA](https://zendesk.atlassian.net/browse/APPS-1493)

/cc @zendesk/quokka