Validate SegmentStore MaxDirectMemory and Cache settings before startup

[abhinb]

Description
We need to make sure that we validate the MaxDirectMemory and Cache values that we configure for the SegmentStore.
As noted in this link, and additionaly, the below invariant for a segment store container should hold before its startup:-

• POD_MEM_LIMIT >= JVM Heap + Direct Memory
• Direct Memory > pravegaservice.cache.size.max ( direct addresable memory by SegemenStore should be greater than the configured cache size preferably 1-2GB more)

If we do not abide by this we can see errors of the form below when SegmentStore starts:-
00:39:19,662 10936089 [core-23] ERROR i.p.s.server.logs.DurableLog - DurableLog[40] Recovery FAILED. io.pravega.segmentstore.storage.cache.CacheFullException: DirectMemoryCache full: Stored = 11788056931, Used = 11811160064, Reserved = 23068672, Allocated = 11811160064, Max = 11811160064

Importance
should-have

Location
SegmentStore container entrypoint script

Suggestions for an improvement
Validate the cache , direct addresable memory and pod memory limit settings before starting up the segment store container and fail fast to avoid issues later when the container starts up.