deprecate log-slow-admin-statements, Better user experience with slow log filters

Hidden server parameter --log-slow-admin-statements

• is not a server variable
• is confusing with variable log_slow_filter=admin

The task would deprecate parameter log-slow-admin-statements, setting is default compile value to yes.

changing log_slow_filter to same usage as optimizer_switch using boolean mode

Reading word filter one expect that admin=yes or just admin means that the server filter admin statements.
What append today is the opposite and that's confusing in itself !

To be consistent we can rename log_slow_filter to log_slow_switch where admin=yes would mean that we don't filter admin statements.

The default would become log_slow_switch="admin=no" to get same content inside slow query log as today