Set Security Dashboard as default from the dashboard itself

Description

With https://gitlab.com/gitlab-org/gitlab-ee/issues/6162 users have the ability to set the Security Dashboard as their default. But this setting is still hard to find, and they may not know it exists.

We could add an actionable item in the Security Dashboard itself to set the parameter, or at least to bring the users to the right place.

Proposal

Add an item (link, button, etc...) to the Security Dashboard to drive the users to set the dashboard as the default one.

If possible, the item will automatically set the default dashboard. Otherwise, it will bring to the right section in User Settings > Preferences > Behavior > Default dashboard.