[web] introduce secondaryHeaderButton prop to Modal component
Summary:
As a preliminary step to introducing the user profile menu component, we need to update the modal component. This diff makes two changes to the Modal component API
- Made the name prop optional
- introduce secondaryHeaderButton
Linear task: https://linear.app/comm/issue/ENG-5190/update-modal-component
Depends on D9447
Test Plan:
Please see the screenshot where I pass in a UserProfileMenu component (will be introduced in a subsequent diff) as the secondaryHeaderButton
Reviewers: atul, inka
Reviewed By: atul
Subscribers: ashoat, tomek, wyilio
Differential Revision: https://phab.comm.dev/D9455