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/plugin_mode.go

@@ -3,6 +3,7 @@ package rendering
 import (
 	"context"
 	"fmt"
+	"time"
 
 	pluginModel "github.com/grafana/grafana-plugin-model/go/renderer"
 )
@@ -22,7 +23,8 @@ func (rs *RenderingService) renderViaPlugin(ctx context.Context, opts Opts) (*Re
 		return nil, err
 	}
 
-	ctx, cancel := context.WithTimeout(ctx, opts.Timeout)
+	// gives plugin some additional time to timeout and return possible errors.
+	ctx, cancel := context.WithTimeout(ctx, opts.Timeout+time.Second*2)
 	defer cancel()
 
 	req := &pluginModel.RenderRequest{