Backend image rendering as plugin (#11966)

* rendering: headless chrome progress

* renderer: minor change

* grpc: version hell

* updated grpc libs

* wip: minor progess

* rendering: new image rendering plugin is starting to work

* feat: now phantomjs works as well and updated alerting to use new rendering service

* refactor: renamed renderer package and service to rendering to make renderer name less confusing (rendering is internal service that handles the renderer plugin now)

* rendering: now render key is passed and render auth is working in plugin mode

* removed unneeded lines from gitignore

* rendering: now plugin mode supports waiting for all panels to complete rendering

* fix: LastSeenAt fix for render calls, was not set which causes a lot of updates to Last Seen at during rendering, this should fix sqlite db locked issues in seen in previous releases

* change: changed render tz url parameter to use proper timezone name as chrome does not handle UTC offset TZ values

* fix: another update to tz param generation

* renderer: added http mode to renderer service, new ini setting [rendering] server_url

pkg/services/rendering/interface.go

@@ -0,0 +1,34 @@
+package rendering
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"github.com/grafana/grafana/pkg/models"
+)
+
+var ErrTimeout = errors.New("Timeout error. You can set timeout in seconds with &timeout url parameter")
+var ErrNoRenderer = errors.New("No renderer plugin found nor is an external render server configured")
+
+type Opts struct {
+	Width    int
+	Height   int
+	Timeout  time.Duration
+	OrgId    int64
+	UserId   int64
+	OrgRole  models.RoleType
+	Path     string
+	Encoding string
+	Timezone string
+}
+
+type RenderResult struct {
+	FilePath string
+}
+
+type renderFunc func(ctx context.Context, options Opts) (*RenderResult, error)
+
+type Service interface {
+	Render(ctx context.Context, opts Opts) (*RenderResult, error)
+}