Add JWT_SECRET environment variable to Docker configurations and update JwtService to use it

docker-compose.dev.yaml

@@ -79,6 +79,7 @@ services:
       ASPNETCORE_URLS: "http://0.0.0.0:8080"
       DOTNET_RUNNING_IN_CONTAINER: "true"
       DB_CONNECTION_STRING: "${DB_CONNECTION_STRING}"
+      JWT_SECRET: "${JWT_SECRET}"
     restart: unless-stopped
     networks:
       - devnet