KB page for GET_LOCK() should be clarified and improved

KB page about GET_LOCK() function (https://mariadb.com/kb/en/library/get_lock/) now says:

"If you have a lock obtained with GET_LOCK(), it is released when you execute RELEASE_LOCK(), execute a new GET_LOCK(), or your connection terminates (either normally or abnormally). Locks obtained with GET_LOCK() do not interact with transactions. That is, committing a transaction does not release any such locks obtained during the transaction.

MariaDB starting with 10.0.2

Konstantin "Kostja" Osipov contributed a patch (MDEV-3917) which allows a user to set many user-level locks in one connection with the GET_LOCK() call."

With the majority of versions users care about now being 10.0.2+ and relying on MDL-based GET_LOCK() implementation we should better describe current behavior (multiple locks per connection, no release of any locks by GET_LOCK() etc in the main text and then add the details about historical behavior as notes.

This KB page also clearly misses examples of outputs from information_schema.metadata_lock_info; when locks are acquired or are waited for by other connection, as well as clear statement that repeatable GET_LOCK('name') calls for the same 'name' in the same connection does not do anything like lock release and re-acquiring of the lock etc.

See also upstream https://bugs.mysql.com/bug.php?id=93043 for some problems in upstream documentation for the function (that we should avoid when adding details).