add isPublic to dashboard (#48012)

adds toggle to make a dashboard public

* config struct for public dashboard config
* api endpoints for public dashboard configuration
* ui for toggling public dashboard on and off
* load public dashboard config on share modal

Co-authored-by: Owen Smallwood <owen.smallwood@grafana.com>
Co-authored-by: Torkel Ödegaard <torkel@grafana.com>

pkg/api/dashboard.go

@@ -146,6 +146,7 @@ func (hs *HTTPServer) GetDashboard(c *models.ReqContext) response.Response {
 		Url:                    dash.GetUrl(),
 		FolderTitle:            "General",
 		AnnotationsPermissions: annotationPermissions,
+		IsPublic:               dash.IsPublic,
 	}
 
 	// lookup folder title