MM-45956: Optimize FileInfo stats query (#22603)

* MM-45956: Optimize FileInfo stats query

We Denormalize Post.ChannelId on FileInfo.ChannelId

```release-note
The file info stats query is now optimized by denormalizing the channelID column into the table itself. This will speed up the query to get the file count for a channel on clicking the RHS.

Migration times:
On a MySQL 8.0.31 DB with
1405 rows in FileInfo and 11M posts, it took around 0.3s

On a Postgres 12.14 DB with
1731 rows in FileInfo and 11M posts, it took around 0.27s
```

https://mattermost.atlassian.net/browse/MM-45956

server/channels/api4/file_test.go

@@ -916,7 +916,7 @@ func TestGetFileLink(t *testing.T) {
 	CheckBadRequestStatus(t, resp)
 
 	// Hacky way to assign file to a post (usually would be done by CreatePost call)
-	err = th.App.Srv().Store().FileInfo().AttachToPost(fileId, th.BasicPost.Id, th.BasicUser.Id)
+	err = th.App.Srv().Store().FileInfo().AttachToPost(fileId, th.BasicPost.Id, th.BasicPost.ChannelId, th.BasicUser.Id)
 	require.NoError(t, err)
 
 	th.App.UpdateConfig(func(cfg *model.Config) { *cfg.FileSettings.EnablePublicLink = false })
@@ -1074,7 +1074,7 @@ func TestGetPublicFile(t *testing.T) {
 	fileId := fileResp.FileInfos[0].Id
 
 	// Hacky way to assign file to a post (usually would be done by CreatePost call)
-	err = th.App.Srv().Store().FileInfo().AttachToPost(fileId, th.BasicPost.Id, th.BasicUser.Id)
+	err = th.App.Srv().Store().FileInfo().AttachToPost(fileId, th.BasicPost.Id, th.BasicPost.ChannelId, th.BasicUser.Id)
 	require.NoError(t, err)
 
 	info, err := th.App.Srv().Store().FileInfo().Get(fileId)
@@ -1139,25 +1139,25 @@ func TestSearchFiles(t *testing.T) {
 	filename := "search for fileInfo1"
 	fileInfo1, appErr := th.App.UploadFile(th.Context, data, th.BasicChannel.Id, filename)
 	require.Nil(t, appErr)
-	err = th.App.Srv().Store().FileInfo().AttachToPost(fileInfo1.Id, th.BasicPost.Id, th.BasicUser.Id)
+	err = th.App.Srv().Store().FileInfo().AttachToPost(fileInfo1.Id, th.BasicPost.Id, th.BasicPost.ChannelId, th.BasicUser.Id)
 	require.NoError(t, err)
 
 	filename = "search for fileInfo2"
 	fileInfo2, appErr := th.App.UploadFile(th.Context, data, th.BasicChannel.Id, filename)
 	require.Nil(t, appErr)
-	err = th.App.Srv().Store().FileInfo().AttachToPost(fileInfo2.Id, th.BasicPost.Id, th.BasicUser.Id)
+	err = th.App.Srv().Store().FileInfo().AttachToPost(fileInfo2.Id, th.BasicPost.Id, th.BasicPost.ChannelId, th.BasicUser.Id)
 	require.NoError(t, err)
 
 	filename = "tagged search for fileInfo3"
 	fileInfo3, appErr := th.App.UploadFile(th.Context, data, th.BasicChannel.Id, filename)
 	require.Nil(t, appErr)
-	err = th.App.Srv().Store().FileInfo().AttachToPost(fileInfo3.Id, th.BasicPost.Id, th.BasicUser.Id)
+	err = th.App.Srv().Store().FileInfo().AttachToPost(fileInfo3.Id, th.BasicPost.Id, th.BasicPost.ChannelId, th.BasicUser.Id)
 	require.NoError(t, err)
 
 	filename = "tagged for fileInfo4"
 	fileInfo4, appErr := th.App.UploadFile(th.Context, data, th.BasicChannel.Id, filename)
 	require.Nil(t, appErr)
-	err = th.App.Srv().Store().FileInfo().AttachToPost(fileInfo4.Id, th.BasicPost.Id, th.BasicUser.Id)
+	err = th.App.Srv().Store().FileInfo().AttachToPost(fileInfo4.Id, th.BasicPost.Id, th.BasicPost.ChannelId, th.BasicUser.Id)
 	require.NoError(t, err)
 
 	archivedChannel := th.CreatePublicChannel()
@@ -1166,7 +1166,7 @@ func TestSearchFiles(t *testing.T) {
 	post := &model.Post{ChannelId: archivedChannel.Id, Message: model.NewId() + "a"}
 	rpost, _, err := client.CreatePost(post)
 	require.NoError(t, err)
-	err = th.App.Srv().Store().FileInfo().AttachToPost(fileInfo5.Id, rpost.Id, th.BasicUser.Id)
+	err = th.App.Srv().Store().FileInfo().AttachToPost(fileInfo5.Id, rpost.Id, rpost.ChannelId, th.BasicUser.Id)
 	require.NoError(t, err)
 	th.Client.DeleteChannel(archivedChannel.Id)