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/apidoc/docs.go

@@ -1398,6 +1398,40 @@ const docTemplate = `{
                 }
             }
         },
+        "/insights/user-status-counts": {
+            "get": {
+                "security": [
+                    {
+                        "CoderSessionToken": []
+                    }
+                ],
+                "produces": [
+                    "application/json"
+                ],
+                "tags": [
+                    "Insights"
+                ],
+                "summary": "Get insights about user status counts",
+                "operationId": "get-insights-about-user-status-counts",
+                "parameters": [
+                    {
+                        "type": "integer",
+                        "description": "Time-zone offset (e.g. -2)",
+                        "name": "tz_offset",
+                        "in": "query",
+                        "required": true
+                    }
+                ],
+                "responses": {
+                    "200": {
+                        "description": "OK",
+                        "schema": {
+                            "$ref": "#/definitions/codersdk.GetUserStatusCountsResponse"
+                        }
+                    }
+                }
+            }
+        },
         "/integrations/jfrog/xray-scan": {
             "get": {
                 "security": [
@@ -11207,6 +11241,20 @@ const docTemplate = `{
                 }
             }
         },
+        "codersdk.GetUserStatusCountsResponse": {
+            "type": "object",
+            "properties": {
+                "status_counts": {
+                    "type": "object",
+                    "additionalProperties": {
+                        "type": "array",
+                        "items": {
+                            "$ref": "#/definitions/codersdk.UserStatusChangeCount"
+                        }
+                    }
+                }
+            }
+        },
         "codersdk.GetUsersResponse": {
             "type": "object",
             "properties": {
@@ -14570,6 +14618,19 @@ const docTemplate = `{
                 "UserStatusSuspended"
             ]
         },
+        "codersdk.UserStatusChangeCount": {
+            "type": "object",
+            "properties": {
+                "count": {
+                    "type": "integer",
+                    "example": 10
+                },
+                "date": {
+                    "type": "string",
+                    "format": "date-time"
+                }
+            }
+        },
         "codersdk.ValidateUserPasswordRequest": {
             "type": "object",
             "required": [