docs: fix five broken commands in the chart README

[aaronmgn]

Summary

Five commands in the chart README do not work. This change corrects them.

Details

• External access: add ingress.enabled="true". The template needs this flag, so the command rendered no Ingress.
• server.conf example: change -Xms2g -Xmx1g to -Xms1g -Xmx2g. The JVM does not start when the start heap is larger than the maximum heap.
• Same example: use --set-string for enableCors and email.enabled. The schema declares both as strings, so --set fails.
• Logging: change statefulset/graylog-app to statefulset/graylog. graylog-app is the container name, not the StatefulSet name.

Linked issues

None.

PR Checklist

Please check the items that apply to your change.

• Tests added/updated
• Documentation updated
• This PR includes a new feature
• This PR includes a bugfix
• This PR includes a refactor

Testing Checklist

Static Validation

• Linter check passes: helm lint ./charts/graylog
• Helm renders local template sucessfully: helm template graylog ./charts/graylog --validate

--validate needs the MongoDB Operator CRD. The test cluster does not have it. helm template without --validate passes.

Installation

• Fresh installation completes successfully: helm install graylog ./charts/graylog
• All pods reach Running state: kubectl rollout status statefulset/graylog
• Helm tests pass: helm test graylog

Functional (if applicable)

• Web UI accessible and login works
• DataNodes visible in System > Cluster Configuration
• Inputs can be created and receive data

Upgrade (if applicable)

• Upgrade from previous release succeeds
• Scaling up/down works correctly
• Configuration changes apply correctly

This change edits only the README. The installation, functional, and upgrade tests did not run.

Specific to this PR

• Ran each corrected command. The ingress command renders 1 Ingress. It rendered 0 before.
• The two --set-string commands template without an error.
• statefulset/graylog is in the rendered output.
• helm unittest passes: 332 tests in 28 suites.

Notes for reviewers

• Verify all applicable tests above pass
• Validate that the linked issues are no longer reproducible, if applicable
• Sync up with the author before merging
• The commit history should be preserved - use rebase-merge or standard merge options when applicable