[Cases] Fix selected label in the assignees filtering (#145113)

## Summary

With the introduction of the "No assignees" filtering in
#143390 we no longer have
assignees for filtering. Having the text say "1 assignee selected" when
selecting the "No assignees" filtering is misleading. This PR fixes this
issue with the label.

<img width="536" alt="Screenshot 2022-11-14 at 3 52 28 PM"
src="https://user-images.githubusercontent.com/7871006/201680341-e007931f-e9d2-4e5f-96d9-0909f4478bc8.png">
<img width="536" alt="Screenshot 2022-11-14 at 3 52 20 PM"
src="https://user-images.githubusercontent.com/7871006/201680344-76b8bf04-8d0e-48ee-97ab-0d860f076f3f.png">
<img width="551" alt="Screenshot 2022-11-14 at 3 51 48 PM"
src="https://user-images.githubusercontent.com/7871006/201680346-a3525a41-cef2-43a9-aa89-7d9238bb3944.png">


### Checklist

Delete any items that are not applicable to this PR.

- [x] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

### For maintainers

- [x] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

x-pack/plugins/cases/public/components/all_cases/assignees_filter.test.tsx

@@ -132,14 +132,32 @@ describe('AssigneesFilterPopover', () => {
 
     await waitFor(async () => {
       userEvent.click(screen.getByTestId('options-filter-popover-button-assignees'));
-      expect(screen.getByText('1 assignee filtered')).toBeInTheDocument();
+      expect(screen.getByText('1 filter selected')).toBeInTheDocument();
     });
 
     await waitForEuiPopoverOpen();
 
     expect(screen.getByText('Damaged Raccoon')).toBeInTheDocument();
   });
 
+  it('shows the total when the multiple users are selected', async () => {
+    const props = {
+      ...defaultProps,
+      selectedAssignees: [userProfiles[0], userProfiles[1]],
+    };
+    appMockRender.render(<AssigneesFilterPopover {...props} />);
+
+    await waitFor(async () => {
+      userEvent.click(screen.getByTestId('options-filter-popover-button-assignees'));
+      expect(screen.getByText('2 filters selected')).toBeInTheDocument();
+    });
+
+    await waitForEuiPopoverOpen();
+
+    expect(screen.getByText('Damaged Raccoon')).toBeInTheDocument();
+    expect(screen.getByText('Physical Dinosaur')).toBeInTheDocument();
+  });
+
   it('shows three users when initially rendered', async () => {
     appMockRender.render(<AssigneesFilterPopover {...defaultProps} />);
 

x-pack/plugins/cases/public/components/all_cases/translations.ts

@@ -127,7 +127,7 @@ export const CLEAR_FILTERS = i18n.translate(
 
 export const TOTAL_ASSIGNEES_FILTERED = (total: number) =>
   i18n.translate('xpack.cases.allCasesView.totalFilteredUsers', {
-    defaultMessage: '{total, plural, one {# assignee} other {# assignees}} filtered',
+    defaultMessage: '{total, plural, one {# filter} other {# filters}} selected',
     values: { total },
   });