fix!: validate HostnameSuffix and SSHConfigOptions' (#26154)

- Adds server-side and client-side validation for
CODER_CONFIGSSH_HOSTNAME_SUFFIX and CODER_SSH_CONFIG_OPTIONS.
- **Server-side breaking change:** invalid values for either of these will cause `coderd` to exit with an error.
- Client-side: `coder config-ssh` will exit with an error if it detects invalid config.
- Adds tests for the above

Local smoke-testing: ran `develop.sh --env-file <path to an env file
containing badness>`. Validated that server startup failed as expected.

> 🤖 Generated by Coder Agents with supervision from a human.

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

cli/configssh.go

@@ -578,6 +578,10 @@ func mergeSSHOptions(
 ) (
 	sshConfigOptions, error,
 ) {
+	if err := coderd.Validate(); err != nil {
+		return sshConfigOptions{}, xerrors.Errorf("invalid ssh config from coderd: %w", err)
+	}
+
 	// Write agent configuration.
 	defaultOptions := []string{
 		"ConnectTimeout=0",