Plugins: Extend panel menu with links from plugins (#63089)

* feat(plugins): introduce dashboard panel menu placement for adding menu items

* test: add test for getPanelMenu()

* added an unique identifier for each extension.

* added context to getPluginExtensions.

* wip

* Wip

* wiwip

* Wip

* feat: WWWIIIIPPPP 🧨

* Wip

* Renamed some of the types to align a bit better.

* added limit to how many extensions a plugin can register per placement.

* decreased number of items to 2

* will trim the lenght of titles to max 25 chars.

* wrapping configure function with error handling.

* added error handling for all scenarios.

* moved extension menu items to the bottom of the more sub menu.

* added tests for configuring the title.

* minor refactorings.

* changed so you need to specify the full path in package.json.

* wip

* removed unused type.

* big refactor to make things simpler and to centralize all configure error/validation handling.

* added missing import.

* fixed failing tests.

* fixed tests.

* revert(extensions): remove static extensions config in favour of registering via AppPlugin APIs

* removed the compose that didn't work for some reason.

* added tests just to verify that validation and error handling is tied together in configuration function.

* adding some more values to the context.

* draft validation.

* added missing tests for getPanelMenu.

* added more tests.

* refactor(extensions): move logic for validating extension link config to function

* Fixed ts errors.

* Update packages/grafana-data/src/types/app.ts

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

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

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

* refactor(extensions): rename limiter -> pluginPlacementCount

* refactor(getpanelmenu): remove redundant continue statement

---------

Co-authored-by: Levente Balogh <balogh.levente.hu@gmail.com>
Co-authored-by: Marcus Andersson <marcus.andersson@grafana.com>

pkg/plugins/manager/loader/loader.go

@@ -333,12 +333,6 @@ 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
 }