Commit message:

MDEV-33144 Implement the Percona variable slow_query_log_always_write_time

This task is inspired by the Percona implementation of
slow_query_log_always_write_time.

This task implements the variable log_slow_always_query_time (name matching
other MariaDB variables using the slow query log). The default value for
the variable is 0, which makes MariaDB compatible with older installations.

For queries with execution time longer than log_slow_always_query_time
the variables log_slow_rate_limit and log_slow_min_examined_row_limit
will not ignored and the query will be written to the slow query log
if there is no other limitations (like log_slow_filter etc).

Other things:

• long_query_time internal variable renamed to log_slow_query_time.
• More descriptive information for "log_slow_query_time".

This code can be found in bb-11.5-monty