Yamcs: No Rate Limiting on Authentication Endpoint

Yamcs is a mission control framework. Prior to 5.12.7, the authentication endpoint POST /auth/token in yamcs-core, handled by yamcs-core/src/main/java/org/yamcs/http/auth/AuthHandler.java, lacked any rate limiting, account lockout, or failed-attempt throttling, so an unauthenticated remote attacker could perform unlimited password-guessing attempts against any user account, significantly increasing the risk of successful brute-force attacks. This issue is fixed in versions 5.12.7 and 5.13.0.