i18n: wires up translations for plugins (#102853)

* i18n: consolidate i18n types & runtime services

* Chore: updates after PR feedback

* Chore: updates after feedback

* Chore: updates after feedback

* Chore: adds feature toggle

* Chore: adds locale to backend

* Chore: adds locales to i18n instance

* Chore: fix missing path in CODEOWNERS

* Chore: fix go lint issues

* Chore: fix missing path in CODEOWNERS

* Chore: updates after PR feedback

* Trigger build

* Chore: updates after PR feedback

* Chore: use resolved language for lookup

* Chore: updates after PR feedback

* Update pkg/plugins/plugins.go

Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

* Chore: updates after PR feedback

* Chore: updates after PR feedback

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Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

pkg/services/featuremgmt/toggles_gen.csv

@@ -239,3 +239,4 @@ alertingMigrationUI,experimental,@grafana/alerting-squad,false,false,true
 unifiedStorageHistoryPruner,experimental,@grafana/search-and-storage,false,false,false
 unifiedStorageGrpcConnectionPool,experimental,@grafana/search-and-storage,false,false,false
 alertingRuleRecoverDeleted,GA,@grafana/alerting-squad,false,false,true
+localizationForPlugins,experimental,@grafana/plugins-platform-backend,false,false,false