Write rate limit value into slow log

TODO: add an example

If log_slow_rate_limit is effective, I would like it is reflected in slow-log for each written query.
It should be written together with log_slow_rate_type

That for in slow log for query we add a section:
# log_slow_rate_type: (session|query) log_slow_rate_limit:1000

Beside that, I would like to add a global variable:
 slow_query_log_always_write_time = N (default: 10 )

This should work in following way:

If log_slow_rate_limit is in effect and query is not going to be written in slow-log
because query is filtered out by rate : we need to check query_time of this query.
and if query_time >= slow_query_log_always_write_time, then we write this query anyway.