Analytics: Track modal dismissal

[loujaybee]

Currently, when triggering a modal close, the dashboard_clicked event is triggered. However, for modal dismissing there is no label property applied, only the path property, making it hard to distinguish between different clicks to dismiss a modal.

Proposal Implement a modal_dismiss tracking event that triggers when a modal is closed in any manner:

1. Use of esc button
2. Close via the X button
3. etc

Relates to this PR: #9663 as part of the epic #6707