docs: update Block Kit Builder links to app.slack.com (#1605)

Author: srtaalej

docs/english/concepts/message-sending.md

@@ -17,7 +17,7 @@ def ask_who(message, say):
 
 `say()` accepts more complex message payloads to make it easy to add functionality and structure to your messages.
 
-To explore adding rich message layouts to your app, read through [the guide on our API site](/messaging/#structure) and look through templates of common app flows [in the Block Kit Builder](https://api.slack.com/tools/block-kit-builder?template=1).
+To explore adding rich message layouts to your app, read through [the guide on our API site](/messaging/#structure) and look through templates of common app flows [in the Block Kit Builder](https://app.slack.com/block-kit-builder).
 
 ```python
 # Sends a section block with datepicker when someone reacts with a 📅 emoji

docs/english/concepts/shortcuts.md

@@ -40,7 +40,7 @@ def open_modal(ack, shortcut, client):
                     "elements": [
                         {
                             "type": "mrkdwn",
-                            "text": "Psssst this modal was designed using <https://api.slack.com/tools/block-kit-builder|*Block Kit Builder*>"
+                            "text": "Psssst this modal was designed using <https://app.slack.com/block-kit-builder|*Block Kit Builder*>"
                         }
                     ]
                 }
@@ -79,7 +79,7 @@ def open_modal(ack, shortcut, client):
                     "elements": [
                         {
                             "type": "mrkdwn",
-                            "text": "Psssst this modal was designed using <https://api.slack.com/tools/block-kit-builder|*Block Kit Builder*>"
+                            "text": "Psssst this modal was designed using <https://app.slack.com/block-kit-builder|*Block Kit Builder*>"
                         }
                     ]
                 }

docs/japanese/concepts/message-sending.md

@@ -16,7 +16,7 @@ def ask_who(message, say):
 
 `say()` は、より複雑なメッセージペイロードを受け付けるので、メッセージに機能やリッチな構造を与えることが容易です。
 
-リッチなメッセージレイアウトをアプリに追加する方法については、[API サイトのガイド](/messaging/#structure)を参照してください。また、[Block Kit ビルダー](https://api.slack.com/tools/block-kit-builder?template=1)の一般的なアプリフローのテンプレートも見てみてください。
+リッチなメッセージレイアウトをアプリに追加する方法については、[API サイトのガイド](/messaging/#structure)を参照してください。また、[Block Kit ビルダー](https://app.slack.com/block-kit-builder)の一般的なアプリフローのテンプレートも見てみてください。
 
 ```python
 # ユーザーが 📅 のリアクションをつけたら、日付ピッカーのついた section ブロックを送信

docs/japanese/concepts/shortcuts.md

@@ -40,7 +40,7 @@ def open_modal(ack, shortcut, client):
                     "elements": [
                         {
                             "type": "mrkdwn",
-                            "text":"Psssst this modal was designed using <https://api.slack.com/tools/block-kit-builder|*Block Kit Builder*>"
+                            "text":"Psssst this modal was designed using <https://app.slack.com/block-kit-builder|*Block Kit Builder*>"
                         }
                     ]
                 }
@@ -80,7 +80,7 @@ def open_modal(ack, shortcut, client):
                     "elements": [
                         {
                             "type": "mrkdwn",
-                            "text":"Psssst this modal was designed using <https://api.slack.com/tools/block-kit-builder|*Block Kit Builder*>"
+                            "text":"Psssst this modal was designed using <https://app.slack.com/block-kit-builder|*Block Kit Builder*>"
                         }
                     ]
                 }