SSH config cannot use SetEnv without multiple problems

[deansheather]

1. The only way to set an env is to use SetEnv=MY_VAR=value. If you use SetEnv MY_VAR=true, the env var gets added to the config incorrectly and SSH fails to load because of bad splitting: https://github.com/coder/vscode-coder/blob/2d7dac8a5f5d9ce2cc6746490c73c8873737034f/src/remote.ts#L716-L733

2. Setting any SetEnv variables causes the default SetEnv CODER_SSH_SESSION_TYPE=vscode to be removed. This is because we use a map to store the key/value pairs.

3. You cannot have multiple SetEnv config lines, only one will be processed.