mod_admin_shell: Add connection created time
This adds an output format option to show the time that the connection was created.
Ref #1852
For full information on our dependencies, version requirements, and
where to find them, see https://prosody.im/doc/depends
If you have luarocks available on your platform, install the following:
- luaexpat
- luasocket
- luafilesystem
- luasec