MDEV-9010 Encryption preset file contains different configuration preset then documentation

* clarify the comment in the preset file
* make boolean --aria-encrypt-tables option to work without an argument

mysql-test/suite/encryption/t/innodb_encryption.opt

---aria-encrypt-tables=ON
---encrypt-tmp-disk-tables=ON
---innodb-encrypt-tables=ON
---innodb-encrypt-log=ON
+--aria-encrypt-tables
+--encrypt-tmp-disk-tables
+--innodb-encrypt-tables
+--innodb-encrypt-log
 --innodb-encryption-rotate-key-age=15
 --innodb-encryption-threads=4
 --innodb-tablespaces-encryption

mysql-test/suite/sys_vars/r/sysvars_aria.result

@@ -56,7 +56,7 @@ NUMERIC_MAX_VALUE	NULL
 NUMERIC_BLOCK_SIZE	NULL
 ENUM_VALUE_LIST	NULL
 READ_ONLY	NO
-COMMAND_LINE_ARGUMENT	REQUIRED
+COMMAND_LINE_ARGUMENT	OPTIONAL
 VARIABLE_NAME	ARIA_FORCE_START_AFTER_RECOVERY_FAILURES
 SESSION_VALUE	NULL
 GLOBAL_VALUE	0

storage/maria/ha_maria.cc

@@ -290,7 +290,7 @@ static MYSQL_SYSVAR_BOOL(used_for_temp_tables,
        "Whether temporary tables should be MyISAM or Aria", 0, 0,
        1);
 
-static MYSQL_SYSVAR_BOOL(encrypt_tables, maria_encrypt_tables, 0,
+static MYSQL_SYSVAR_BOOL(encrypt_tables, maria_encrypt_tables, PLUGIN_VAR_OPCMDARG,
        "Encrypt tables (only for tables with ROW_FORMAT=PAGE (default) "
        "and not FIXED/DYNAMIC)",
        0, 0, 0);

support-files/rpm/enable_encryption.preset

@@ -4,8 +4,12 @@
 # ensure that everything that can be encrypted will be and your
 # data will not leak unencrypted.
 #
-# If in the future more encryption related options will be implemented,
-# this file will enable them too.
+# DO NOT EDIT THIS FILE! On MariaDB upgrades it might be replaced with a
+# newer version and your edits will be lost. Instead, add your edits
+# to the .cnf file after the !include directive.
+#
+# NOTE that you also need to install an encryption plugin for the encryption
+# to work. See https://mariadb.com/kb/en/mariadb/data-at-rest-encryption/#encryption-key-management
 #
 [mariadb]
 aria-encrypt-tables