Update new issue form to match Pajamas specs

What does this MR do and why?

Issue: #333730 (closed)

This makes the following changes to the new Issue form:

• do not disable the submit button when the form is invalid
• display Pajamas style error messages when submitting an invalid form
• mark required fields with an asterisk

Screenshots or screen recordings

before (submitted)	after (not yet submitted)	after (submitted)

How to set up and validate locally

Go to the new issue form and click 'Create issue'

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.