[ML] Changes for optional spaces plugin (#151170)

Changes to ensure ML behaves correctly when the spaces plugin is
disabled.
Related to #149687
Closes #149953

ML was in pretty good shape for this change as we already assumed spaces
could be optional.
The only change needed is to ensure the saved object sync button is
enabled on the management page even when spaces is missing.
Previously we incorrectly hid this button.

x-pack/plugins/ml/public/application/components/ml_saved_objects_spaces_list/ml_saved_objects_spaces_list.tsx

@@ -19,7 +19,7 @@ import { useMlApiContext } from '../../contexts/kibana';
 import { useToastNotificationService } from '../../services/toast_notification_service';
 
 interface Props {
-  spacesApi: SpacesPluginStart;
+  spacesApi: SpacesPluginStart; // this component is only ever used when spaces is enabled
   spaceIds: string[];
   id: string;
   mlSavedObjectType: MlSavedObjectType;

x-pack/plugins/ml/public/application/contexts/kibana/kibana_context.ts

@@ -40,7 +40,7 @@ interface StartPlugins {
   usageCollection?: UsageCollectionSetup;
   fieldFormats: FieldFormatsRegistry;
   dashboard: DashboardSetup;
-  spacesApi: SpacesPluginStart;
+  spacesApi?: SpacesPluginStart;
   charts: ChartsPluginStart;
   cases?: CasesUiStart;
   unifiedSearch: UnifiedSearchPublicPluginStart;

x-pack/plugins/ml/public/application/management/jobs_list/components/jobs_list_page/jobs_list_page.tsx

@@ -62,7 +62,6 @@ export const JobsListPage: FC<{
     () => mlApiServicesProvider(new HttpService(coreStart.http)),
     [coreStart.http]
   );
-  const spacesEnabled = spacesApi !== undefined;
   const [initialized, setInitialized] = useState(false);
   const [accessDenied, setAccessDenied] = useState(false);
   const [isPlatinumOrTrialLicense, setIsPlatinumOrTrialLicense] = useState(true);
@@ -153,20 +152,18 @@ export const JobsListPage: FC<{
                 >
                   <EuiFlexGroup>
                     <EuiFlexItem grow={false}>
-                      {spacesEnabled && (
-                        <>
-                          <EuiButtonEmpty
-                            onClick={() => setShowSyncFlyout(true)}
-                            data-test-subj="mlStackMgmtSyncButton"
-                          >
-                            {i18n.translate('xpack.ml.management.jobsList.syncFlyoutButton', {
-                              defaultMessage: 'Synchronize saved objects',
-                            })}
-                          </EuiButtonEmpty>
-                          {showSyncFlyout && <JobSpacesSyncFlyout onClose={onCloseSyncFlyout} />}
-                          <EuiSpacer size="s" />
-                        </>
-                      )}
+                      <>
+                        <EuiButtonEmpty
+                          onClick={() => setShowSyncFlyout(true)}
+                          data-test-subj="mlStackMgmtSyncButton"
+                        >
+                          {i18n.translate('xpack.ml.management.jobsList.syncFlyoutButton', {
+                            defaultMessage: 'Synchronize saved objects',
+                          })}
+                        </EuiButtonEmpty>
+                        {showSyncFlyout && <JobSpacesSyncFlyout onClose={onCloseSyncFlyout} />}
+                        <EuiSpacer size="s" />
+                      </>
                     </EuiFlexItem>
                     <EuiFlexItem grow={false}>
                       <ExportJobsFlyout

x-pack/plugins/ml/public/application/management/jobs_list/components/jobs_list_page/space_management/space_management.tsx

@@ -32,7 +32,7 @@ import { getFilters } from './filters';
 import { useTableState } from './use_table_state';
 
 interface Props {
-  spacesApi: SpacesPluginStart | undefined;
+  spacesApi?: SpacesPluginStart;
   setCurrentTab: (tabId: MlSavedObjectType) => void;
 }