[AI assisted] MM-62837: (#30268)

We did not invalidate the cache after converting a user to bot.
That led to issues. See JIRA for more details.

https://mattermost.atlassian.net/browse/MM-62837

```release-note
NONE
```

server/channels/app/bot.go

@@ -617,6 +617,7 @@ func (a *App) ConvertUserToBot(rctx request.CTX, user *model.User) (*model.Bot,
 	if err := a.RevokeAllSessions(rctx, user.Id); err != nil {
 		return nil, err
 	}
+	a.InvalidateCacheForUser(user.Id)
 
 	return bot, nil
 }