mgr/dashboard: move monitoring tabs to a single page

mgr/dashboard: move monitoring tabs to a single page

with a tab for 'active alerts', 'all alerts' and 'silences'. Due to
ambiguity with existing names, `AlertListComponent` has been renamed to
`ActiveAlertListComponent`. Introduces `MonitoringListComponent` as
first page for monitoring concerns, using path `/monitoring`.

Keeps the activated tab open, independent of the way that's used to go
back to the previous page, be it the cancel button or submit button or
the link on the breadcrumb. Also keeps the active tab open even when the
page is reloaded.

Fixes: https://tracker.ceph.com/issues/42877
Signed-off-by: Patrick Seidensal <pseidensal@suse.com>