HPCC-11637 Revise based on review comments

(1) Make ActivityInfo cache time configurable (default to 10 seconds);
(2) Remove extra code for ActivityInfo object clear; (3) Create a new
method getActivityInfo: check whether cached ActivityInfo is valid. If
not, update the cache with latest Activity Info. Return the valid cache;
(4) Response is populated outside of the getActivityInfo().

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>