Updated installation ofcode-server to be consistent with the other templates using the same method as#6138

This fixes an error where thestderr stream ofcode-server wasn't correctly redirected to the log file

WARNING: script exited successfully, but output pipes were not closed after 10s. This usually means a child process was started with references to stdout or stderr. As a result, this process may now have been terminated. Consider redirecting the output or using a separate "coder_script" for the process, seehttps://coder.com/docs/templates/troubleshooting#startup-script-issues for more information.

Also updated the image used in the "inner container" of theenvbox template and removed unnecessarysensitive designation on template variables.

I tested the new template to verify it creates a workspace without error. I verified thatsystemd anddocker appear to be working normally in the workspace.