Plugins: expose getBackendSrv() to plugins (#15268)

Temporarily expose getBackendSrv while we figure out a long term solution.  This will unblock developing some more complex react external plugins.

public/app/features/plugins/plugin_loader.ts

@@ -23,6 +23,7 @@ import * as datemath from 'app/core/utils/datemath';
 import * as fileExport from 'app/core/utils/file_export';
 import * as flatten from 'app/core/utils/flatten';
 import * as ticks from 'app/core/utils/ticks';
+import { BackendSrv, getBackendSrv } from 'app/core/services/backend_srv';
 import impressionSrv from 'app/core/services/impression_srv';
 import builtInPlugins from './built_in_plugins';
 import * as d3 from 'd3';
@@ -93,6 +94,16 @@ exposeToPlugin('app/features/dashboard/impression_store', {
   __esModule: true,
 });
 
+/**
+ * NOTE: this is added temporarily while we explore a long term solution
+ * If you use this export, only use the:
+ *  get/delete/post/patch/request methods
+ */
+exposeToPlugin('app/core/services/backend_srv', {
+  BackendSrv,
+  getBackendSrv,
+});
+
 exposeToPlugin('app/plugins/sdk', sdk);
 exposeToPlugin('app/core/utils/datemath', datemath);
 exposeToPlugin('app/core/utils/file_export', fileExport);