fix: support passwordless Redis by conditionally building auth segment

[Steffen911]

Summary

• Fixes the REDIS_CONNECTION_STRING to conditionally include the auth segment based on whether redis.auth.password and redis.auth.username are configured
• When both are set to null, the connection string omits the auth segment entirely (e.g., redis://host:port/db)
• Allows connections to Redis instances without authentication (e.g., AWS ElastiCache without auth)

Behavior Matrix

redis.auth.password	redis.auth.username	Connection String
"mypass"	"default"	redis://default:$(REDIS_PASSWORD)@host:port/db
"mypass"	null	redis://:$(REDIS_PASSWORD)@host:port/db
null	"default"	redis://default@host:port/db
null	null	redis://host:port/db

Test plan

• Added 4 new test cases for passwordless Redis scenarios
• All 52 helm unit tests pass
• Verified connection string output with helm template for each scenario

Fixes #291, fixes #273

🤖 Generated with Claude Code

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Important

Supports passwordless Redis by conditionally omitting auth segment in connection string based on configuration.

• Behavior:
  • Updates REDIS_CONNECTION_STRING in _helpers.tpl to conditionally include auth segment based on redis.auth.password and redis.auth.username.
  • Omits auth segment if both are null, allowing passwordless Redis connections.
  • Supports Redis instances without authentication, such as AWS ElastiCache.
• Configuration:
  • Updates values.yaml to clarify redis.auth.password and redis.auth.username usage for passwordless connections.
  • Modifies README.md to reflect changes in Redis authentication configuration.
• Testing:
  • Adds 4 test cases in redis-cluster_test.yaml for passwordless Redis scenarios.
  • Verifies connection string output with helm template for each scenario.

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[github-actions]

Helm Unit Test Results

52 tests  +4   52 ✅ +4   2s ⏱️ ±0s
 9 suites ±0    0 💤 ±0 
 1 files   ±0    0 ❌ ±0 

Results for commit baf48e1. ± Comparison against base commit cab27df.