CL-1: Add MySQL Router connection limits

[szachovy]

Problem

MySQL Router is bootstrapped with default settings. No max_connections limit means all MySQL server connections can be consumed by a single misbehaving client, starving cluster operations (health checks, replication, admin).

File: services/mysql-mgmt/docker_compose.yml

Fix

After mysqlrouter --bootstrap completes, inject connection limits into the generated mysqlrouter.conf:

sed -i 's/\[routing:bootstrap_rw\]/[routing:bootstrap_rw]\nmax_connections=40/' \
    /opt/default/mysql_router/mysqlrouter.conf

This reserves connections for cluster operations (replication, health checks, admin).

Acceptance Criteria

• Post-bootstrap step injects max_connections=40 into routing:bootstrap_rw section of mysqlrouter.conf
• Connections reserved for cluster operations (replication, health checks, admin)
• Router restart handled if required