feat(redis): add support for specifying external Redis username

[RangerRick]

TL;DR: Additional changes related to #428

Newer versions of Redis support configuring multiple users each with their own password.
This adds support for optionally specifying the username when making connections.

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This pull request adds support for Redis username configuration (for Redis 6 and above) across the Diode Helm chart, server, and related files. This allows deployments to connect to Redis instances that require a username, which is important for environments using Redis ACLs. The chart version is also bumped to 1.10.0.

Redis username support:

• Added username field to externalRedis configuration in charts/diode/values.yaml and documented it in charts/diode/README.md. The username is now required when using an external Redis and is passed into the environment and templates. [1] [2] [3]
• Updated _helpers.tpl to create and validate the Redis username value, ensuring it's defined when redis.enabled is false.
• Updated ConfigMap templates (diode-ingester-configmap.yaml, diode-reconciler-configmap.yaml) to include REDIS_USERNAME environment variable. [1] [2]

Server and application changes:

• Added RedisUsername to config structs in both diode-server/ingester/config.go and diode-server/reconciler/config.go, and updated the main application logic to use the username when connecting to Redis. [1] [2] [3] [4] [5]
• Updated Docker Compose and sample env files to include REDIS_USERNAME for both ingester and reconciler services. [1] [2] [3]

Testing and environment:

• Updated test setup and teardown in component_test.go and reconciler_test.go to set and unset REDIS_USERNAME environment variable. [1] [2] [3] [4]

Version bump:

• Bumped chart version to 1.10.0 in Chart.yaml and updated the README badge. [1] [2]

[github-actions]

Go test coverage

STATUS	ELAPSED	PACKAGE	COVER	PASS	FAIL	SKIP
🟢 PASS	1.19s	github.com/netboxlabs/diode/diode-server/auth	44.7%	42	0	0
🟢 PASS	0.21s	github.com/netboxlabs/diode/diode-server/auth/cli	0.0%	0	0	0
🟢 PASS	1.01s	github.com/netboxlabs/diode/diode-server/authutil	82.8%	5	0	0
🟢 PASS	0.00s	github.com/netboxlabs/diode/diode-server/dbstore/postgres	0.0%	0	0	0
🟢 PASS	1.11s	github.com/netboxlabs/diode/diode-server/entityhash	86.7%	16	0	0
🟢 PASS	0.00s	github.com/netboxlabs/diode/diode-server/errors	0.0%	0	0	0
🟢 PASS	1.33s	github.com/netboxlabs/diode/diode-server/ingester	82.7%	25	0	0
🟢 PASS	1.05s	github.com/netboxlabs/diode/diode-server/migrator	70.4%	4	0	0
🟢 PASS	4.14s	github.com/netboxlabs/diode/diode-server/netboxdiodeplugin	83.6%	40	0	0
🟢 PASS	2.60s	github.com/netboxlabs/diode/diode-server/reconciler	82.7%	86	0	0
🟢 PASS	1.01s	github.com/netboxlabs/diode/diode-server/reconciler/applier	85.7%	1	0	0
🟢 PASS	0.00s	github.com/netboxlabs/diode/diode-server/reconciler/changeset	0.0%	0	0	0
🟢 PASS	1.07s	github.com/netboxlabs/diode/diode-server/reconciler/differ	63.8%	6	0	0
🟢 PASS	1.02s	github.com/netboxlabs/diode/diode-server/server	85.7%	14	0	0
🟢 PASS	1.02s	github.com/netboxlabs/diode/diode-server/telemetry	28.0%	26	0	0
🟢 PASS	1.02s	github.com/netboxlabs/diode/diode-server/telemetry/otel	91.7%	25	0	0
🟢 PASS	0.00s	github.com/netboxlabs/diode/diode-server/tls	0.0%	0	0	0
🟢 PASS	1.01s	github.com/netboxlabs/diode/diode-server/version	100.0%	2	0	0

Total coverage: 53.9%

[mfiedorowicz]

LGTM, thank you