Expose folder UID in dashboards API response (#33991) (#34772)

* expose folder UID in dashboards API response, import dashboards into folders by folder UID

* handle bad folder UID as 400 error

* 12591:Add tests for request with folderUid

* Use more descriptive error status for missing folders

Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>

* return 400 when folder id is missing

* put error checking in the right place this time

* mention folderUid in the docs

* Clarify usage of folderUid and folderId when both present

Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>

* Capitalise UID

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

* mention folder UID in the metadata for a GET response

Co-authored-by: Ida Furjesova <ida.furjesova@grafana.com>
Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>
Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>
(cherry picked from commit ef0fab9aa5)

Co-authored-by: Serge Zaitsev <serge.zaitsev@grafana.com>

pkg/models/dashboards.go

@@ -339,6 +339,7 @@ type SaveDashboardCommand struct {
 	RestoredFrom int              `json:"-"`
 	PluginId     string           `json:"-"`
 	FolderId     int64            `json:"folderId"`
+	FolderUid    string           `json:"folderUid"`
 	IsFolder     bool             `json:"isFolder"`
 
 	UpdatedAt time.Time