* add recently deleted dashboards

* adds user guide for removing unused dashboards

* apply suggestions from review

bolding UI text, avoid temporal words, etc.

Co-authored-by: Jorie Helwig <jorie.helwig@datadoghq.com>

* fix bold list titles, spacing

* change title

* adds "open in notebook"

Co-authored-by: Jorie Helwig <jorie.helwig@datadoghq.com>