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/store/localcachelayer/channel_layer_test.go

@@ -104,6 +104,43 @@ func TestChannelStoreChannelMemberCountsCache(t *testing.T) {
 	})
 }
 
+func TestChannelStoreChannelsMemberCountCache(t *testing.T) {
+	channelsCountResult := map[string]int64{
+		"channel1": 10,
+		"channel2": 20,
+	}
+
+	t.Run("first call not cached, second cached and returning same data", func(t *testing.T) {
+		mockStore := getMockStore()
+		mockCacheProvider := getMockCacheProvider()
+		cachedStore, err := NewLocalCacheLayer(mockStore, nil, nil, mockCacheProvider)
+		require.NoError(t, err)
+
+		channelsCount, err := cachedStore.Channel().GetChannelsMemberCount([]string{"channel1", "channel2"})
+		require.NoError(t, err)
+		assert.Equal(t, channelsCount, channelsCountResult)
+		mockStore.Channel().(*mocks.ChannelStore).AssertNumberOfCalls(t, "GetChannelsMemberCount", 1)
+		channelsCount, err = cachedStore.Channel().GetChannelsMemberCount([]string{"channel1", "channel2"})
+		require.NoError(t, err)
+		assert.Equal(t, channelsCount, channelsCountResult)
+		mockStore.Channel().(*mocks.ChannelStore).AssertNumberOfCalls(t, "GetChannelsMemberCount", 1)
+	})
+
+	t.Run("first call not cached, invalidate cache, second call not cached", func(t *testing.T) {
+		mockStore := getMockStore()
+		mockCacheProvider := getMockCacheProvider()
+		cachedStore, err := NewLocalCacheLayer(mockStore, nil, nil, mockCacheProvider)
+		require.NoError(t, err)
+
+		cachedStore.Channel().GetChannelsMemberCount([]string{"channel1", "channel2"})
+		mockStore.Channel().(*mocks.ChannelStore).AssertNumberOfCalls(t, "GetChannelsMemberCount", 1)
+		cachedStore.Channel().InvalidateMemberCount("channel1")
+		cachedStore.Channel().InvalidateMemberCount("channel2")
+		cachedStore.Channel().GetChannelsMemberCount([]string{"channel1", "channel2"})
+		mockStore.Channel().(*mocks.ChannelStore).AssertNumberOfCalls(t, "GetChannelsMemberCount", 2)
+	})
+}
+
 func TestChannelStoreChannelPinnedPostsCountsCache(t *testing.T) {
 	countResult := int64(10)