MDEV-23114 AUTH_PAM plugin can not be disabled when using mysql_release config

When setting the PLUGIN_AUTH_PAM variable, mark it as a "CACHE" variable
so it can be overridden by the user.

cmake/build_configurations/mysql_release.cmake

@@ -118,7 +118,7 @@ ENDIF()
 
 IF(UNIX)
   SET(WITH_EXTRA_CHARSETS all CACHE STRING "")
-  SET(PLUGIN_AUTH_PAM YES)
+  SET(PLUGIN_AUTH_PAM YES CACHE BOOL "")
 
   IF(CMAKE_SYSTEM_NAME STREQUAL "Linux")
     IF(NOT IGNORE_AIO_CHECK)