Docker: Run Telegraf as non-root

The Telegraf 1.20.3 release has changed its official DockerHub image to no longer run the Telegraf service as root. This change enhances security given the wide extensibility and array of plugins available in Telegraf, aligning with best practices from both Docker's published guidelines and the Center for Internet Security (CIS) Docker Benchmark. Users may need to modify how they use the Telegraf Docker image due to this change, ensuring that the telegraf user or group has access to any additional required services, sockets, files, etc., for operation.