Add SSL/TLS support for Redis connections

[BenCodez]

Summary

• add opt-in Redis.SSL support for backend (Paper/Spigot), BungeeCord, and Velocity Redis connections
• apply TLS consistently to both Redis subscribers and the proxy's dedicated publisher pool
• add MultiProxyRedis.SSL for separate multi-proxy Redis connections
• preserve existing plaintext behavior by default
• validate Redis certificates with the JVM truststore and verify hostnames
• document the new settings in the bundled YAML configurations
• add unit coverage for TLS-enabled and default plaintext client configuration

Configuration

Redis:
  SSL: true

For a separate multi-proxy connection:

MultiProxyRedis:
  SSL: true

When MultiProxyRedis.UseExistingConnection is true, the primary Redis.SSL value applies.

Verification

• mvn test on Java 21: 297 tests passed, 0 failures, 0 errors
• both YAML resource files parse successfully
• whitespace validation passed
• dynamic CodeQL analysis completed successfully

Dependency

Depends on BenCodez/SimpleAPI#72. Merge and publish/rebuild that snapshot before building this PR.

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