fix: replace Instance Settings with Default Settings in i18n and docs (#8143)

# Which Problems Are Solved

- The console shows the Instance Settings title and a description.
Instance settings should be replaced with Default settings

# How the Problems Are Solved

- The DESCRIPTIONS.SETTINGS.INSTANCE.TITLE and
DESCRIPTIONS.SETTINGS.INSTANCE.DESCRIPTION have been replaced with
Default Settings and in the corresponding translation files.

Here's a screenshot:


![image](https://github.com/zitadel/zitadel/assets/30386061/b404f209-2043-414c-b06d-3291771d54fb)

# Additional Changes

- The docs have been updated to replace remaining texts mentioning
Instance Settings with Default Settings
- Two unused texts have been deleted from the translation files
- VSCode with Prettier have applied some markdown changes

# Additional Context

- Closes #7632

---------

Co-authored-by: Fabi <[email protected]>

console/src/assets/i18n/ja.json

@@ -79,8 +79,8 @@
     },
     "SETTINGS": {
       "INSTANCE": {
-        "TITLE": "インスタンス設定",
-        "DESCRIPTION": "インスタンス設定は、すべての組織のデフォルト設定です。適切な権限があれば、いくつかは組織の設定で上書き可能です。"
+        "TITLE": "デフォルトの設定",
+        "DESCRIPTION": "すべての組織のデフォルト設定。適切な権限があれば、一部の権限は組織設定で上書きできます。"
       },
       "ORG": {
         "TITLE": "組織設定",
@@ -1317,10 +1317,6 @@
     }
   },
   "SETTINGS": {
-    "INSTANCE": {
-      "TITLE": "インスタンス設定",
-      "DESCRIPTION": "これらの設定は上書きされていない限り、すべての組織に適用されます。"
-    },
     "LIST": {
       "ORGS": "組織",
       "FEATURESETTINGS": "機能設定",