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>

webapp/platform/client/src/client4.ts

@@ -1755,6 +1755,13 @@ export default class Client4 {
         );
     };
 
+    getChannelsMemberCount = (channelIds: string[]) => {
+        return this.doFetch<Record<string, number>>(
+            `${this.getChannelsRoute()}/stats/member_count`,
+            {method: 'post', body: JSON.stringify(channelIds)}
+        )
+    }
+
     getChannelModerations = (channelId: string) => {
         return this.doFetch<ChannelModeration[]>(
             `${this.getChannelRoute(channelId)}/moderations`,

webapp/platform/types/src/channels.ts

@@ -156,6 +156,7 @@ export type ChannelsState = {
     channelModerations: RelationOneToOne<Channel, ChannelModeration[]>;
     channelMemberCountsByGroup: RelationOneToOne<Channel, ChannelMemberCountsByGroup>;
     messageCounts: RelationOneToOne<Channel, ChannelMessageCount>;
+    channelsMemberCount: Record<string, number>;
 };
 
 export type ChannelModeration = {