fix: update .env.sample for CE v3.x SMTP requirements and add config versions

.env.sample

@@ -7,5 +7,20 @@ DOMAIN=plausible.example.com
 LETS_ENCRYPT_ENV=production
 
 SECRET_KEY_BASE=replace-me
-DISABLE_AUTH=replace-me # true or false
-DISABLE_REGISTRATION=replace-me # true or false
+DISABLE_AUTH=false
+DISABLE_REGISTRATION=true
+
+## SMTP settings (required — SMTP_HOST_PORT must be an integer)
+SMTP_HOST_ADDR=localhost
+MAILER_EMAIL=noreply@plausible.example.com
+SMTP_HOST_PORT=25
+#SMTP_USER_NAME=
+#SMTP_USER_PWD=
+SMTP_HOST_SSL_ENABLED=false
+
+## Config object versions (increment when config file content changes)
+CLICKHOUSE_CONF_VERSION=v1
+CLICKHOUSE_USER_CONF_VERSION=v1
+CLICKHOUSE_ENTRYPOINT_VERSION=v1
+PG_BACKUP_VERSION=v1
+CLICKHOUSE_BACKUP_SCRIPT_VERSION=v1