feat(coderd/database): track user status changes over time (#16019)

RE: https://github.com/coder/coder/issues/15740,
https://github.com/coder/coder/issues/15297

In order to add a graph to the coder frontend to show user status over
time as an indicator of license usage, this PR adds the following:

* a new `api.insightsUserStatusCountsOverTime` endpoint to the API
* which calls a new `GetUserStatusCountsOverTime` query from postgres
* which relies on two new tables `user_status_changes` and
`user_deleted`
* which are populated by a new trigger and function that tracks updates
to the users table

The chart itself will be added in a subsequent PR

---------

Co-authored-by: Mathias Fredriksson <mafredri@gmail.com>

coderd/database/dbauthz/dbauthz_test.go

@@ -1708,6 +1708,12 @@ func (s *MethodTestSuite) TestUser() {
 			rbac.ResourceTemplate.InOrg(orgID), policy.ActionRead,
 		)
 	}))
+	s.Run("GetUserStatusCounts", s.Subtest(func(db database.Store, check *expects) {
+		check.Args(database.GetUserStatusCountsParams{
+			StartTime: time.Now().Add(-time.Hour * 24 * 30),
+			EndTime:   time.Now(),
+		}).Asserts(rbac.ResourceUser, policy.ActionRead)
+	}))
 }
 
 func (s *MethodTestSuite) TestWorkspace() {