Signal K Server Vulnerable to Denial of Service via Unrestricted Access Request Flooding

Signal K Server is a server application that runs on a central hub in a boat. A Denial of Service (DoS) vulnerability in versions prior to 2.19.0 allows an unauthenticated attacker to crash the SignalK Server by flooding the access request endpoint (`/signalk/v1/access/requests`). This causes a "JavaScript heap out of memory" error due to unbounded in-memory storage of request objects. Version 2.19.0 fixes the issue.