feat: add support for TLS protocol to Redis connection (rediss://)

[dreglad]

What this PR does / why we need it

• Introduces a tls configuration option under zammadConfig.redis (defaulting to false for backwards compatibility).
• Updates the REDIS_URL in _helpers.tpl to dynamically use the rediss:// protocol schema when TLS is enabled, instead of hardcoding redis://.
• This fixes connectivity issues and enables native SSL/TLS connections when connecting Zammad to external Redis instances, or configuring Redis subchart to use TLS/SSL.

Special notes for your reviewer

• Helm template generation was tested locally and correctly provisions rediss:// only when tls: true.

Checklist

• Chart Version bumped

[mgruner]

Thanks and 👏 @dreglad