Plugins: Support for link extensions (#61663)

* added extensions to plugin.json and exposing it via frontend settings.

* added extensions to the plugin.json schema.

* changing the extensions in frontend settings to a map instead of an array.

* wip

* feat(pluginregistry): begin wiring up registry

* feat(pluginextensions): prevent duplicate links and clean up

* added test case for link extensions.

* added tests and implemented the getPluginLink function.

* wip

* feat(pluginextensions): expose plugin extension registry

* fix(pluginextensions): appease the typescript gods post rename

* renamed file and will throw error if trying to call setExtensionsRegistry if trying to call it twice.

* added reafactorings.

* fixed failing test.

* minor refactorings to make sure we only include extensions if the app is enabled.

* fixed some nits.

* Update public/app/features/plugins/extensions/registry.test.ts

Co-authored-by: Levente Balogh <balogh.levente.hu@gmail.com>

* Update packages/grafana-runtime/src/services/pluginExtensions/registry.ts

Co-authored-by: Levente Balogh <balogh.levente.hu@gmail.com>

* Update packages/grafana-runtime/src/services/pluginExtensions/registry.ts

Co-authored-by: Levente Balogh <balogh.levente.hu@gmail.com>

* Update public/app/features/plugins/extensions/registry.test.ts

Co-authored-by: Levente Balogh <balogh.levente.hu@gmail.com>

* Moved types for extensions from data to runtime.

* added a small example on how you could consume link extensions.

* renamed after feedback from levi.

* updated the plugindef.cue.

* using the generated plugin def.

* added tests for apps and extensions.

* fixed linting issues.

* wip

* wip

* wip

* wip

* test(extensions): fix up failing tests

* feat(extensions): freeze registry extension arrays, include type in registry items

* added restrictions in the pugindef cue schema.

* wip

* added required fields.

* added key to uniquely identify each item.

* test(pluginextensions): align tests with implementation

* chore(schema): refresh reference.md

---------

Co-authored-by: Jack Westbrook <jack.westbrook@gmail.com>
Co-authored-by: Levente Balogh <balogh.levente.hu@gmail.com>

pkg/plugins/manager/loader/loader.go

@@ -334,6 +334,12 @@ func (l *Loader) readPluginJSON(pluginJSONPath string) (plugins.JSONData, error)
 		}
 	}
 
+	for i, extension := range plugin.Extensions {
+		if !filepath.IsAbs(extension.Path) {
+			plugin.Extensions[i].Path = path.Join("/", extension.Path)
+		}
+	}
+
 	return plugin, nil
 }