Docs: Skip loading en-US translations in loadResources example

[shelldandy]

Summary

• Updates the loadResources.ts code sample in the plugin i18n guide to import DEFAULT_LANGUAGE from @grafana/i18n and add an early return when the resolved language is the default
• This avoids unnecessary dynamic imports of ~500kb of en-US translations that are already embedded in source code via t() and <Trans>

Related: grafana/logs-drilldown#1839
Related: grafana/grafana#122188

Test plan

• Code sample compiles and reads correctly in context of the guide

[github-actions]

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[Copilot]

Pull request overview

This PR updates the Grafana 11 plugin internationalization guide to avoid loading translation resources for the default language, since default-language strings are already provided inline via t() and <Trans>.

Changes:

• Update the loadResources.ts example to import DEFAULT_LANGUAGE from @grafana/i18n.
• Add an early return in loadResources when resolvedLanguage is the default language to skip the dynamic import.