HPCC-12012 Cache PackageMaps/PackageSets info in WsPackageProcess

The PackageMaps/PackageSets info is cached into WsPackageProcess
in order to avoid unecessary calls to dali. Subscribe/notify is
used for dali to notify the ESP service about possible changes
of the PackageMaps/PackageSets info.

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>
Should this be a get rather than query?  If the caller doesn't own the tree, it could disappear if someone else updates the cache.