feat: add preStop lifecycle hook for replication mode

[peins94]

Description

Replication mode pods currently have no preStop lifecycle hook, unlike cluster mode.
When a master pod is terminated during a rolling update or node drain, clients experience
downtime until Sentinel detects the failure and triggers a failover (up to down-after-milliseconds).
This adds a preStop hook for the replication role following the same pattern as the existing
cluster mode hook in generateClusterPreStop. The hook:

1. Checks if the terminating pod is the master via INFO replication
2. Derives the Sentinel headless service from the pod hostname
3. Triggers SENTINEL FAILOVER mymaster
4. Waits up to 30 seconds for the role to change to slave
   Replica pods skip the hook entirely.

Type of change

• New feature (non-breaking change which adds functionality)

Checklist

• Tests have been added/modified and all tests pass.
• Functionality/bugs have been confirmed to be unchanged or fixed.
• I have performed a self-review of my own code.
• Documentation has been updated or added where necessary.

Additional Context

In production we observed that every rolling restart of a RedisReplication StatefulSet causes
client downtime because the master pod is killed without failover. This is particularly
impactful for large datasets where replica startup takes 30-40 minutes, as Sentinel may
trigger unnecessary full resyncs while the topology is unstable.