optimize export sync plans, and clear too many sync plans

src/langs/en.json

@@ -38,7 +38,10 @@
   "protocol_onedrive_connect_unknown": "Do not know how to deal with the callback: {{params}}",
   "command_startsync": "start sync",
   "command_drynrun": "start sync (dry run only)",
-  "command_exportsyncplans_json": "export sync plans in json format",
+  "command_exportsyncplans_1": "export sync plans (latest 1)",
+  "command_exportsyncplans_5": "export sync plans (latest 5)",
+  "command_exportsyncplans_all": "export sync plans (all)",
+
   "command_exportlogsindb": "export logs saved in db",
 
   "statusbar_time_years": "Synced {{time}} years ago",
@@ -292,7 +295,9 @@
   "settings_viewconsolelog_desc": "On desktop, please press \"ctrl+shift+i\" or \"cmd+shift+i\" to view the log. On mobile, please install the third-party plugin <a href='https://obsidian.md/plugins?search=Logstravaganza'>Logstravaganza</a> to export the console log to a note.",
   "settings_syncplans": "Export Sync Plans",
   "settings_syncplans_desc": "Sync plans are created every time after you trigger sync and before the actual sync. Useful to know what would actually happen in those sync. Click the button to export sync plans.",
-  "settings_syncplans_button_json": "Export",
+  "settings_syncplans_button_1": "Export latest 1",
+  "settings_syncplans_button_5": "Export latest 5",
+  "settings_syncplans_button_all": "Export All",
   "settings_syncplans_notice": "Sync plans history exported.",
   "settings_delsyncplans": "Delete Sync Plans History In DB",
   "settings_delsyncplans_desc": "Delete sync plans history in DB.",