As a Jira user writing automation rules

I want a rule validated prior to save

So I can create automation more effectively

Acceptance criteria:

• At save, the smart value syntax is validated. Errors are shown next to the rule components.
• At save, the rule components are validated for missing parts. Errors are shown next to the rule components.
• Bonus: where smart values can be entered, auto-completion is provided to reduce entry errors.
• Bonus: where null values can short-circuit smart values, warnings are shown