Cfg: Add a setting to configure if the local file system is available (#83616)

* Introduce environment.local_filesystem_available

* Only show TLS client cert, client key, client ca when local_filesystem_available is true

* Rename LocalFSAvailable to LocalFileSystemAvailable

pkg/api/frontendsettings.go

@@ -220,6 +220,7 @@ func (hs *HTTPServer) getFrontendSettings(c *contextmodel.ReqContext) (*dtos.Fro
 		PublicDashboardsEnabled:             hs.Cfg.PublicDashboardsEnabled,
 		SharedWithMeFolderUID:               folder.SharedWithMeFolderUID,
 		RootFolderUID:                       accesscontrol.GeneralFolderUID,
+		LocalFileSystemAvailable:            hs.Cfg.LocalFileSystemAvailable,
 
 		BuildInfo: dtos.FrontendSettingsBuildInfoDTO{
 			HideVersion:   hideVersion,