publicdashboards: split create/update api paths (#57940)

This PR splits the create and update paths for public dashboards and includes assorted refactors toward a proper REST API. Additionally, we removed the concept of a "public dashboard config" in favor of "public dashboard" 

Co-authored-by: juanicabanas <juan.cabanas@grafana.com>
Co-authored-by: Ezequiel Victorero <ezequiel.victorero@grafana.com>

pkg/api/dtos/dashboard.go

@@ -32,6 +32,7 @@ type DashboardMeta struct {
 	Provisioned                bool                  `json:"provisioned"`
 	ProvisionedExternalId      string                `json:"provisionedExternalId"`
 	AnnotationsPermissions     *AnnotationPermission `json:"annotationsPermissions"`
+	HasPublicDashboard         bool                  `json:"hasPublicDashboard"`
 	PublicDashboardAccessToken string                `json:"publicDashboardAccessToken"`
 	PublicDashboardUID         string                `json:"publicDashboardUid"`
 	PublicDashboardEnabled     bool                  `json:"publicDashboardEnabled"`