MDEV-28819 Statically compiled encryption plugins do not work in mariadb-backup

Disable static build for encryption plugin file_key_management

plugin/file_key_management/CMakeLists.txt

 SET(FILE_KEY_MANAGEMENT_PLUGIN_SOURCES file_key_management_plugin.cc parser.cc)
 
 INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR}/sql)
-MYSQL_ADD_PLUGIN(FILE_KEY_MANAGEMENT ${FILE_KEY_MANAGEMENT_PLUGIN_SOURCES})
+MYSQL_ADD_PLUGIN(FILE_KEY_MANAGEMENT ${FILE_KEY_MANAGEMENT_PLUGIN_SOURCES} MODULE_ONLY)