Alerting: Fix image rendering and uploading timeout preventing to send alert notifications (#21536)

* svc alerting - use a shorter ctx to upload the img
This will prevent timeout on img upload to cancel the notifications from being sent

* components img uploader - pass the ctx to aws lib

* make webdavuploader use the ctx

* make azureblobuploader use the ctx

* rename uploadImage() to renderAndUploadImage()
for better clarity about what this method work

* Use timeout + 2s for plugin renderer (same as service and phantomjs)

* Make sure that original EvalContext is updated after render and upload

* Verify notification sent even if render or image upload times out

* fix lint

* fixes after review

Co-authored-by: Edouard Hur <3418467+hekmon@users.noreply.github.com>

Fixes #21018

pkg/services/rendering/phantomjs.go

@@ -63,6 +63,7 @@ func (rs *RenderingService) renderViaPhantomJS(ctx context.Context, opts Opts) (
 		cmdArgs = append([]string{fmt.Sprintf("--output-encoding=%s", opts.Encoding)}, cmdArgs...)
 	}
 
+	// gives phantomjs some additional time to timeout and return possible errors.
 	commandCtx, cancel := context.WithTimeout(ctx, opts.Timeout+time.Second*2)
 	defer cancel()