Add log level support and decrease info level verbosity

[michaelprice232]

Description

Aims to resolve #700

Following an investigation into log levels in our CI K8s cluster - which uses ephemeral CI runners so there are lots of pod create events - we uncovered the following:

• The k8s-metadata-injection app was the heaviest logger out of all the nri-bundle components we use
• For each pod create event there are 5 INFO level logs generated, which could lead to a performance overhead on larger clusters
• There was no log level support (defaults to INFO)
• In one of the logs userinfo is being returned at INFO level which might not be desirable in some environments

This PR aims to address the above concerns by:

1. Adding log level support
2. Dropping the existing 5 INFO level logs to DEBUG level
3. Add a new single INFO level log which provides a summary

Also updated the Helm chart to add the new environment variable - NEW_RELIC_K8S_METADATA_INJECTION_LOG_LEVEL - which defaults to INFO level.

Added some basic unit and Helm tests. As part of manual testing locally I deployed the config into a Minikube cluster and then provisioned some pods.

Using the default INFO log level:

$ k logs nri-metadata-injection-6cfb7f868-gtzwf                                                                                                                                                   
{"level":"info","ts":"2026-02-11T16:17:25.767Z","caller":"server/main.go:83","msg":"starting the TLS readiness server"}
{"level":"info","ts":"2026-02-11T16:17:25.768Z","caller":"server/main.go:98","msg":"starting the webhook server"}
{"level":"info","ts":"2026-02-11T16:19:42.168Z","caller":"server/webhook.go:160","msg":"admission review received","operation":"CREATE","kind":"Pod","namespace":"default","podGenerateName":"nginx-66686b6766-","uid":"6d45b223-0f54-48c7-910f-fc994517596d","mutate":true}

Using the DEBUG log level you can see the previous log entries which have been left untouched.

I noted there are some docs which explicitly call out the log line entries. I've added a PR for that repo: newrelic/docs-website#23044.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• New feature / enhancement (non-breaking change which adds functionality)
• Security fix
• Bug fix (non-breaking change which fixes an issue)

Checklist:

• Add changelog entry following the contributing guide
• Documentation has been updated
• This change requires changes in testing:
  • unit tests
  • E2E tests