feat: Add support for update checks and notifications (#4810)

Co-authored-by: Kira Pilot <kira@coder.com>

coderd/database/databasefake/databasefake.go

@@ -119,9 +119,10 @@ type data struct {
 	workspaceResources        []database.WorkspaceResource
 	workspaces                []database.Workspace
 
-	deploymentID  string
-	derpMeshKey   string
-	lastLicenseID int32
+	deploymentID    string
+	derpMeshKey     string
+	lastUpdateCheck []byte
+	lastLicenseID   int32
 }
 
 func (fakeQuerier) IsFakeDB() {}
@@ -3272,6 +3273,24 @@ func (q *fakeQuerier) GetDERPMeshKey(_ context.Context) (string, error) {
 	return q.derpMeshKey, nil
 }
 
+func (q *fakeQuerier) InsertOrUpdateLastUpdateCheck(_ context.Context, data string) error {
+	q.mutex.RLock()
+	defer q.mutex.RUnlock()
+
+	q.lastUpdateCheck = []byte(data)
+	return nil
+}
+
+func (q *fakeQuerier) GetLastUpdateCheck(_ context.Context) (string, error) {
+	q.mutex.RLock()
+	defer q.mutex.RUnlock()
+
+	if q.lastUpdateCheck == nil {
+		return "", sql.ErrNoRows
+	}
+	return string(q.lastUpdateCheck), nil
+}
+
 func (q *fakeQuerier) InsertLicense(
 	_ context.Context, arg database.InsertLicenseParams,
 ) (database.License, error) {