Support `SetEnv TERM` since ssh supports it now

[jace]

I've installed Ghostty and have a similar problem as with Kitty in #469. Ghostty sets $TERM to xterm-ghostty, which is not a known terminal type in remote environments. Here are their suggested fixes.

I've setup ~/.ssh/config to reset TERM for all remote connections (supported since openssh 8.7):

Host *
  SetEnv TERM=xterm-256color

This now works for ssh <anywhere> but not for et <anywhere>. Looks like et is ignoring this setting. From the log:

[INFO 2024-12-27 14:40:44,218 client-main ParseConfigFile.hpp:1405] unsupported config line: SetEnv TERM=xterm-256color, ignored [V1 2024-12-27 14:40:44,345 client-main SshSetupHandler.cpp:78] Trying ssh with args: [email protected] echo 'XXXDq79V6QkGBNuu/C7MgQP3w9I6bbEPGPxK94rZYASiz5a0s_xterm-ghostty' | etterminal --verbose=9

Support for SetEnv TERM on par with ssh would be nice.

[jace]

I've found a workaround with a conditional alias in my shell config:

[[ "$TERM" =~ "xterm-(ghostty|kitty)" ]] && alias et='TERM=xterm-256color et'