br: remove cloud admin filter from br restoration and set --with-sys-…

…table as default value (#15897)

br/backup-and-restore-overview.md

@@ -125,7 +125,7 @@ Backup and restore might go wrong when some TiDB features are enabled or disable
 
 Before performing backup and restore, BR compares the TiDB cluster version with its own and checks their compatibility. If the versions are incompatible, BR reports an error and exits. To forcibly skip the version check, you can set `--check-requirements=false`. Note that skipping the version check might introduce incompatibility in data.
 
-Starting from v7.0.0, TiDB gradually supports performing backup and restore operations through SQL statements. Therefore, it is strongly recommended to use the BR tool of the same major version as the TiDB cluster when backing up and restoring cluster data, and avoid performing data backup and restore operations across major versions. This helps ensure smooth execution of restore operations and data consistency.
+Starting from v7.0.0, TiDB gradually supports performing backup and restore operations through SQL statements. Therefore, it is strongly recommended to use the BR tool of the same major version as the TiDB cluster when backing up and restoring cluster data, and avoid performing data backup and restore operations across major versions. This helps ensure smooth execution of restore operations and data consistency. Starting from v7.6.0, BR restores data in some `mysql` system tables by default, that is, the `--with-sys-table` option is set to `true` by default. When restoring data to a TiDB cluster with a different version, if you encounter an error similar to `[BR:Restore:ErrRestoreIncompatibleSys]incompatible system table` due to different schemas of system tables, you can set `--with-sys-table=false` to skip restoring the system tables and avoid this error.
 
 The compatibility information for BR before TiDB v6.6.0 is as follows:
 

br/br-snapshot-guide.md

@@ -121,7 +121,9 @@ tiup br restore full \
 
 ### Restore tables in the `mysql` schema
 
-Starting from BR v5.1.0, when you back up snapshots, BR backs up the **system tables** in the `mysql` schema and does not restore them by default. Starting from BR v6.2.0, BR restores **data in some system tables** if you configure `--with-sys-table`.
+- Starting from BR v5.1.0, when you back up snapshots, BR automatically backs up the **system tables** in the `mysql` schema, but does not restore these system tables by default. 
+- Starting from v6.2.0, BR lets you specify `--with-sys-table` to restore **data in some system tables**. 
+- Starting from v7.6.0, BR enables `--with-sys-table` by default, which means that BR restores **data in some system tables** by default.
 
 **BR can restore data in the following system tables:**
 
@@ -169,7 +171,7 @@ Starting from BR v5.1.0, when you back up snapshots, BR backs up the **system ta
 
 When you restore data related to system privilege, note the following:
 
-- BR does not restore user data with `user` as `cloud_admin` and `host` as `'%'`. This user is reserved for TiDB Cloud. Do not create a user or role named `cloud_admin` in your cluster, because the user privileges related to `cloud_admin` cannot be restored correctly.
+- Before v7.6.0, BR does not restore user data with `user` as `cloud_admin` and `host` as `'%'`. This user is reserved for TiDB Cloud. Starting from v7.6.0, BR supports restoring all user data (including `cloud_admin`) by default.
 - Before restoring data, BR checks whether the system tables in the target cluster are compatible with those in the backup data. "Compatible" means that all the following conditions are met:
 
     - The target cluster has the same system tables as the backup data.