Add key to header modals to force remount on modal close

[blackjackkent]

Description

Adds key to header modals to force remount on modal close.

Motivation and Context

Modal was retaining info from previous form submission when reopened (if a user was adding multiple threads at once).

How Has This Been Tested?

UAT.

Screenshots (if appropriate):

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.