TS should have the ability to keep a minimum number of connections active for all keep alive cases

Today, TS keeps a keep alive connection to the Origin Server upto the time thats specified in
proxy.config.http.keep_alive_no_activity_timeout_out in the case that the connection hasnt been re-used for that period
of time.
In addition to that, it would be nice to be able to say that if a connection has been opened, keep atleast 'n' number
of connections open to the OS regardless of the fact that the connection hasnt been used for a while.
Obviously 'n' has to be a small number so that we dont end up holding up too many connections to the OS unnecessarily,
since this feature is simply to allow requests that come after that period of time to still enjoy the benefits of YCPI
reducing the impact of TCP's 3-way HandShake (especially over a long distance).
Also, do note, that a connection close event from the Origin Server should obviously be handled correctly and the
connection should be removed from the pool. In that case, no new connections have to be re-opened to maintain 'n'. This
can purely be done on demand.