MM42267: Add member count in the browse channel modal (#23800)

* add base for calling the endpoint

* add endpoint and handler

* update store and layers

* call the endpoint

* align types

* update app layers

* generate mocks

* complete handler

* finish store query

* add todos

* add ui for member count

* add selector

* add a todo

* add cache layer

* optimize calls in FE

* handle invalidation of the cache

* fix go style

* fix test

* use existing channel layer count

* fix import error

* delete unnecessary code

* write tests for channel cache layer

* fix testname

* fix mocks

* fix cache layer test

* fix a test

* really fix the test

* write more tests for server

* address PR comments

* remove comment

* rename more_channels to browse_channels

* fix style

* update snapshot

* add translations

* Revert "add translations"

This reverts commit 56476a5dabe357703ef02be9a38b3e88f5c8b1e7.

* add only related translations

* address PR review points

* add test

* fix test

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/channel_test.go

@@ -2195,6 +2195,24 @@ func TestGetMemberCountsByGroup(t *testing.T) {
 	require.ElementsMatch(t, cmc, resp)
 }
 
+func TestGetChannelsMemberCount(t *testing.T) {
+	th := SetupWithStoreMock(t)
+	defer th.TearDown()
+
+	mockStore := th.App.Srv().Store().(*mocks.Store)
+	mockChannelStore := mocks.ChannelStore{}
+	channelsMemberCount := map[string]int64{
+		"channel1": int64(10),
+		"channel2": int64(20),
+	}
+	mockChannelStore.On("GetChannelsMemberCount", []string{"channel1", "channel2"}).Return(channelsMemberCount, nil)
+	mockStore.On("Channel").Return(&mockChannelStore)
+	mockStore.On("GetDBSchemaVersion").Return(1, nil)
+	resp, err := th.App.GetChannelsMemberCount(th.Context, []string{"channel1", "channel2"})
+	require.Nil(t, err)
+	require.Equal(t, channelsMemberCount, resp)
+}
+
 func TestViewChannelCollapsedThreadsTurnedOff(t *testing.T) {
 	th := Setup(t).InitBasic()
 	defer th.TearDown()