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.go

@@ -225,6 +225,35 @@ func (s LocalCacheChannelStore) SaveMultipleMembers(members []*model.ChannelMemb
 	return members, nil
 }
 
+func (s LocalCacheChannelStore) GetChannelsMemberCount(channelIDs []string) (_ map[string]int64, err error) {
+	counts := make(map[string]int64)
+	remainingChannels := make([]string, 0)
+
+	for _, channelID := range channelIDs {
+		var cacheItem int64
+		err := s.rootStore.doStandardReadCache(s.rootStore.channelMemberCountsCache, channelID, &cacheItem)
+		if err == nil {
+			counts[channelID] = cacheItem
+		} else {
+			remainingChannels = append(remainingChannels, channelID)
+		}
+	}
+
+	if len(remainingChannels) > 0 {
+		remainingChannels, err := s.ChannelStore.GetChannelsMemberCount(remainingChannels)
+		if err != nil {
+			return nil, err
+		}
+
+		for id, count := range remainingChannels {
+			s.rootStore.doStandardAddToCache(s.rootStore.channelMemberCountsCache, id, count)
+			counts[id] = count
+		}
+	}
+
+	return counts, nil
+}
+
 func (s LocalCacheChannelStore) UpdateMember(member *model.ChannelMember) (*model.ChannelMember, error) {
 	member, err := s.ChannelStore.UpdateMember(member)
 	if err != nil {