Ticket 51072 - improve autotune defaults
    
    Bug Description: we have learnt that the CPU autotuning is too aggresive, potentially
    decreasing throughput due to overhead in context switching and lock contention, and
    that our memory tuning is not aggressive enough, at only 10% of the system memory.
    Additionally, in containers, we are able to have access to different memory limits
    and reservations, so we can choose to be even more forward in our selection.
    
    Fix Description: Change thread tuning to match the number of threads available on
    the system. Change memory tuning to 25% of system memory by default. Finally add
    an environment variable to containers allowing more aggressive tuning to be
    set DS_MEMORY_PERCENTAGE. Later this could be set to a higher default value.
    
    https://pagure.io/389-ds-base/issue/51072
    
    Author: William Brown <william@blackhats.net.au>
    
    Review by: mreynolds, vashirov, tbordaz (Thanks!)