fix(frontend): change placeholder in chat bar (#2177)

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

frontend/public/locales/en/chat.json

@@ -1,5 +1,5 @@
 {
-  "actions_bar_placeholder": "Ask a question to a @brain and choose your #prompt",
+  "actions_bar_placeholder": "Ask a question",
   "add_document": "Add document",
   "ask": "Ask a question, or describe a task.",
   "back_to_search": "Back to search",
@@ -63,4 +63,4 @@
   "tooManyRequests": "You have exceeded the number of requests per day. To continue chatting, please upgrade your account or come back tomorrow.",
   "welcome": "Welcome",
   "yesterday": "Yesterday"
-}
+}

frontend/public/locales/es/chat.json

@@ -1,5 +1,5 @@
 {
-  "actions_bar_placeholder": "Haz una pregunta a un @cerebro y elige tu #prompt",
+  "actions_bar_placeholder": "Escribe un mensaje...",
   "add_document": "Agregar documento",
   "ask": "Has una pregunta o describe un tarea.",
   "back_to_search": "Volver a la búsqueda",

frontend/public/locales/fr/chat.json

@@ -1,5 +1,5 @@
 {
-  "actions_bar_placeholder": "Posez une question à un @cerveau et sélectionnez un #prompt ",
+  "actions_bar_placeholder": "Posez une question",
   "add_document": "Ajouter un document",
   "ask": "Posez une question ou décrivez une tâche.",
   "back_to_search": "Retour à la recherche",

frontend/public/locales/pt-br/chat.json

@@ -1,5 +1,5 @@
 {
-  "actions_bar_placeholder": "Faça uma pergunta a um @cérebro e escolha sua #prompt",
+  "actions_bar_placeholder": "Faça uma pergunta",
   "add_document": "Adicionar documento",
   "ask": "Faça uma pergunta ou descreva uma tarefa.",
   "back_to_search": "Voltar para a pesquisa",

frontend/public/locales/ru/chat.json

@@ -1,5 +1,5 @@
 {
-  "actions_bar_placeholder": "Задайте вопрос @мозгу и выберите свой #подсказка",
+  "actions_bar_placeholder": "Введите сообщение...",
   "add_document": "Добавить документ",
   "ask": "Задайте вопрос или опишите задачу.",
   "back_to_search": "Вернуться к поиску",

frontend/public/locales/zh-cn/chat.json

@@ -1,5 +1,5 @@
 {
-  "actions_bar_placeholder": "向 @大脑 提问，选择您的 #提示",
+  "actions_bar_placeholder": "在这里添加一个动作",
   "add_document": "添加文件",
   "ask": "提一个问题，或描述一个任务。",
   "back_to_search": "返回搜索",